Hyperventilation syndrome (HVS); also chronic hyperventilation syndrome (CHVS) and dysfunctional breathing hyperventilation syndrome is a respiratory disorder, psychologically or physiologically based, involving breathing too deeply or too rapidly (hyperventilation). HVS may present with chest pain and a tingling sensation in the fingertips and around the mouth (paresthesia) and may accompany a panic attack.

People with HVS may feel that they cannot get enough air. In reality, they have about the same oxygenation in the arterial blood (normal values are about 98% for hemoglobin saturation) and too little carbon dioxide (hypocapnia) in their blood and other tissues. While oxygen is abundant in the bloodstream, HVS reduces effective delivery of that oxygen to vital organs due to low--induced vasoconstriction and the suppressed Bohr effect.

The hyperventilation is self-promulgating as rapid breathing causes carbon dioxide levels to fall below healthy levels, and respiratory alkalosis (high blood pH) develops. This makes the symptoms worse, which causes the person to try breathing even faster, which further exacerbates the problem.

The respiratory alkalosis leads to changes in the way the nervous system fires and leads to the paresthesia, dizziness, and perceptual changes that often accompany this condition. Other mechanisms may also be at work, and some people are physiologically more susceptible to this phenomenon than others.

Hyperventilation syndrome is a remarkably common cause of dizziness complaints. About 25% of patients who complain about dizziness are diagnosed with HVS.

A diagnostic Nijmegen Questionnaire provides an accurate diagnosis of Hyperventilation.

In medicine, hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate ("hypo" meaning "below") to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapnia) and respiratory acidosis. Hypoventilation is not synonymous with respiratory arrest, in which breathing ceases entirely and death occurs within minutes due to hypoxia and leads rapidly into complete anoxia, although both are medical emergencies. Hypoventilation can be considered a precursor to hypoxia and its lethality is attributed to hypoxia with carbon dioxide toxicity.

Lightheadedness is a common and typically unpleasant sensation of dizziness and/or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel as though his or her head is weightless. The individual may also feel as though the room is what causes the "spinning" or moving (vertigo) associated with lightheadedness. Most causes of lightheadedness are not serious and either cure themselves quickly, or are easily treated.

Keeping a sense of balance requires the brain to process a variety of information received from the eyes, the nervous system, and the inner ears. If the brain is unable to process these signals, such as when the messages are contradictory, or if the sensory systems are improperly functioning, an individual may experience lightheadedness or dizziness.

Hypoventilation may be caused by:

- A medical condition such as stroke affecting the brainstem

- Voluntary breath-holding or underbreathing, for example, hypoventilation training or Buteyko

- Medication or drugs, typically when taken in accidental or intentional overdose. Opioids in particular are known to cause respiratory depression. Examples of opioids include pharmaceuticals such as oxycodone and hydromorphone.

- Hypocapnia, which stimulates hypoventilation

- Chronic mountain sickness, a mechanism to conserve energy.

Lightheadedness can be simply (and most commonly) an indication of a temporary shortage of blood or oxygen to the brain due to a drop in blood pressure, rapid dehydration from vomiting, diarrhea, or fever. Other causes are: low blood sugar, hyperventilation, Postural Orthostatic Tachycardia Syndrome, panic attacks, and anemia. It can also be a symptom of many other conditions, some of them serious, such as heart problems (including abnormal heart rhythm or heart attack), respiratory problems such as pulmonary embolism, and also stroke, bleeding, and shock. If any of these serious disorders is present, the individual will usually have additional symptoms such as chest pain, a feeling of a racing heart, loss of speech or change in vision.

Many people, especially as they age, experience lightheadedness if they arise too quickly from a lying or seated position. Lightheadedness often accompanies the flu, hypoglycaemia, common cold, or allergies.

Dizziness could be provoked by the use of antihistamine drugs, like levocetirizine or by some antibiotics or SSRIs. Nicotine or tobacco products can cause lightheadedness for inexperienced users. Narcotic drugs, such as codeine can also cause lightheadedness.

Signs and symptoms of respiratory alkalosis are as follows:

- Palpitation

- Tetany

- Convulsion

- Sweating

The American Thoracic Society defines dyspnea as: "A subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity." Other definitions describe it as "difficulty in breathing", "disordered or inadequate breathing", "uncomfortable awareness of breathing", and as the experience of "breathlessness" (which may be either acute or chronic).

Patients who suffer from acute OI usually manifest the disorder by a temporary loss of consciousness and posture, with rapid recovery (simple faints, or syncope), as well as remaining conscious during their loss of posture. This is different from a syncope caused by cardiac problems because there are known triggers for the fainting spell (standing, heat, emotion) and identifiable prodromal symptoms (nausea, blurred vision, headache). As Dr. Julian M. Stewart, an expert in OI from New York Medical College states, "Many syncopal patients have no intercurrent illness; between faints, they are well."

Symptoms:

- Altered vision (blurred vision, "white outs"/gray outs, black outs, double vision)

- Anxiety

- Exercise intolerance

- Fatigue

- Headache

- Heart palpitations, as the heart races to compensate for the falling blood pressure

- Hyperpnea or sensation of difficulty breathing or swallowing (see also hyperventilation syndrome)

- Lightheadedness

- Sweating

- Tremulousness

- Weakness

A classic manifestation of acute OI is a soldier who faints after standing rigidly at attention for an extended period of time.

Patients with chronic orthostatic intolerance have symptoms on most or all days. Their symptoms may include most of the symptoms of acute OI, plus:

- Nausea

- Neurocognitive deficits, such as attention problems

- Pallor

- Sensitivity to heat

- Sleep problems

- Other vasomotor symptoms.

Many conditions are associated with dizziness. Dizziness can accompany certain serious events, such as a concussion or brain bleed, epilepsy and seizures (convulsions), strokes, and cases of meningitis and encephalitis. However, the most common subcategories can be broken down as follows: 40% peripheral vestibular dysfunction, 10% central nervous system lesion, 15% psychiatric disorder, 25% presyncope/disequilibrium, and 10% nonspecific dizziness. Some vestibular pathologies have symptoms that are comorbid with mental disorders. The medical conditions that often have dizziness as a symptom include:

- Benign paroxysmal positional vertigo

- Meniere's disease

- Vestibular neuronitis

- Labyrinthitis

- Otitis media

- Brain tumor

- Acoustic neuroma

- Motion sickness

- Ramsay Hunt syndrome

- Migraine

- Multiple sclerosis

- Pregnancy

- low blood pressure (hypotension)

- low blood oxygen content (hypoxemia)

- heart attack

- iron deficiency (anemia)

- low blood sugar (hypoglycemia)

- hormonal changes (e.g. thyroid disease, menstruation, pregnancy)

- panic disorder

- hyperventilation

- anxiety

- depression

- age-diminished visual, balance, and perception of spatial orientation abilities

There are two types of respiratory alkalosis: chronic and acute as a result of the 3-5 day delay in kidney compensation of the abnormality.

- "Acute respiratory alkalosis" occurs rapidly, have a high pH because the response of the kidneys is slow.

- "Chronic respiratory alkalosis" is a more long-standing condition, here one finds the kidneys have time to decrease the bicarbonate level.

While shortness of breath is generally caused by disorders of the cardiac or respiratory system, other systems such as neurological, musculoskeletal, endocrine, hematologic, and psychiatric may be the cause. DiagnosisPro, an online medical expert system, listed 497 distinct causes in October 2010. The most common cardiovascular causes are acute myocardial infarction and congestive heart failure while common pulmonary causes include chronic obstructive pulmonary disease, asthma, pneumothorax, pulmonary edema and pneumonia. On a pathophysiological basis the causes can be divided into: (1) an increased awareness of normal breathing such as during an anxiety attack, (2) an increase in the work of breathing and (3) an abnormality in the ventilatory system.

Symptoms and signs of early hypercapnia include flushed skin, full pulse, tachypnea, dyspnea, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure. According to other sources, symptoms of mild hypercapnia might include headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmias. Hypercapnia may increase pulmonary capillary resistance. In severe hypercapnia (generally PaCO greater than 10 kPa or 75 mmHg), symptomatology progresses to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death.

Hypercapnia, also known as hypercarbia and CO retention, is a condition of abnormally elevated carbon dioxide (CO) levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs.

Hypercapnia normally triggers a reflex which increases breathing and access to oxygen (O), such as arousal and turning the head during sleep. A failure of this reflex can be fatal, for example as a contributory factor in sudden infant death syndrome.

Hypercapnia is the opposite of hypocapnia, the state of having abnormally reduced levels of carbon dioxide in the blood. Hypercapnia is from the Greek "hyper" = "above" or "too much" and "kapnos" = "smoke".

Palpitations are the perceived abnormality of the heartbeat characterized by awareness of cardiac muscle contractions in the chest: hard, fast and/or irregular beats. It is both a symptom reported by the patient and a medical diagnosis. Palpitation can be associated with anxiety and does not necessarily indicate a structural or functional abnormality of the heart, but it can be a symptom arising from an objectively rapid or irregular heartbeat. Palpitation can be intermittent and of variable frequency and duration, or continuous. Associated symptoms include dizziness, shortness of breath, sweating, headaches, and chest pain.

Palpitation may be associated with coronary heart disease, hyperthyroidism, diseases affecting cardiac muscle such as hypertrophic cardiomyopathy, diseases causing low blood oxygen such as asthma and emphysema; previous chest surgery; kidney disease; low levels of brain serotonin; blood loss, and pain; drugs such as antidepressants, statins, alcohol, nicotine, caffeine, cocaine, and amphetamines; electrolyte imbalances of magnesium, potassium and calcium; and deficiencies of nutrients such as taurine, arginine, and iron.

It might be expected that people with E.I.B. would present with shortness of breath, and/or an elevated respiratory rate and wheezing, consistent with an asthma attack. However, many will present with decreased stamina, or difficulty in recovering from exertion compared to team members, or paroxysmal coughing from an irritable airway. Similarly, examination may reveal wheezing and prolonged expiratory phase, or may be quite normal. Consequently, a potential for under-diagnosis exists. Measurement of airflow, such as peak expiratory flow rates, which can be done inexpensively on the track or sideline, may prove helpful.

When people experience panic attacks, they are convinced that they are about to die or suffer some extreme calamity in which some kind of action is done by the individual (such as fleeing or screaming). In case of phobophobia, a panic attack might be encountered as the fear that they will in fact experience the calamities of the feared phobia and see it as something inevitable. Also, the nature of the panic is of profound personal significance to the individual, on a similar way phobophobia is related to the individual. This is why panic attacks are closely related to phobophobia.

Nevertheless, they can differentiate themselves by the fact that phobophobia is a psychological fear of the phobia itself that intensifies it, while panic attacks are extreme fear of encountering the calamities of an imminent disaster, and in this particular case, of encountering other phobias, which can be often accompanied by the at least four of the following common symptoms of panic attacks:

1. Dyspnea

2. Palpitations

3. Chest pain or discomfort

4. Choking or smothering sensations

5. Vertigo or unsteady feelings

6. Feelings of unreality (depersonalization or derealization)

7. Paresthesias (tingling in hands or feet)

8. Hot and cold flushes

9. Faintness

10. Trembling or shaking

11. Difficult breathing

12. Sweating

Panic attacks can also be accompanied by disturbance in heart action and feelings of desperation and angst. Being closely related, phobophobia and panic attacks, the first one can be treated like a panic attack with psychological therapy. Moreover, in combination with phobophobia, a patient might be more susceptible to believe that their continuing anxiety symptoms will eventually culminate in a much more severe mental disorder, such as schizophrenia.

Exercise-induced asthma, or E.I.A., occurs when the airways narrow as a result of exercise. The preferred term for this condition is exercise-induced bronchoconstriction (EIB); exercise does not cause asthma, but is frequently an asthma trigger.

Three common descriptions of "palpitation" are "flip-flopping" (or "stop and start"), often caused by premature contraction of the atrium or ventricle, with the perceived "stop" from the pause following the contraction, and the "start" from the subsequent forceful contraction; rapid "fluttering in the chest," with regular "fluttering" suggesting supraventricular or ventricular arrhythmias (including sinus tachycardia) and irregular "fluttering" suggesting atrial fibrillation, atrial flutter, or tachycardia with variable block; and "pounding in the neck" or neck pulsations, often due to "cannon" A waves in the jugular venous pulsations that occur when the right atrium contracts against a closed tricuspid valve.

Palpitation associated with chest pain suggests coronary artery disease, or if the chest pain is relieved by leaning forward, pericardial disease is suspected. Palpitation associated with light-headedness, fainting or near fainting suggest low blood pressure and may signify a life-threatening abnormal heart rhythm. Palpitation that occurs regularly with exertion suggests a rate-dependent bypass tract or hypertrophic cardiomyopathy. If a benign cause for these concerning symptoms cannot be found at the initial visit, then ambulatory monitoring or prolonged heart monitoring in the hospital might be warranted. Noncardiac symptoms should also be elicited since the palpitations may be caused by a normal heart responding to a metabolic or inflammatory condition. Weight loss suggests hyperthyroidism. Palpitation can be precipitated by vomiting or diarrhea that leads to electrolyte disorders and hypovolemia. Hyperventilation, hand tingling, and nervousness are common when anxiety or panic disorder is the cause of the palpitations.

Many people being treated for panic attacks begin to experience limited symptom attacks. These panic attacks are less comprehensive, with fewer than four bodily symptoms being experienced.

It is not unusual to experience only one or two symptoms at a time, such as vibrations in their legs, shortness of breath, or an intense wave of heat traveling up their bodies, which is not similar to hot flashes due to estrogen shortage. Some symptoms, such as vibrations in the legs, are sufficiently different from any normal sensation that they clearly indicate panic disorder. Other symptoms on the list can occur in people who may or may not have panic disorder. Panic disorder does not require four or more symptoms to all be present at the same time. Causeless panic and racing heartbeat are sufficient to indicate a panic attack.

People with panic attacks often report a fear of dying or heart attack, flashing vision, faintness or nausea, numbness throughout the body, heavy breathing and hyperventilation, or loss of body control. Some people also suffer from tunnel vision, mostly due to blood flow leaving the head to more critical parts of the body in defense. These feelings may provoke a strong urge to escape or flee the place where the attack began (a consequence of the "fight-or-flight response", in which the hormone causing this response is released in significant amounts). This response floods the body with hormones, particularly epinephrine (adrenaline), which aid it in defending against harm.

A panic attack is a response of the sympathetic nervous system (SNS). The most common symptoms include trembling, dyspnea (shortness of breath), heart palpitations, chest pain (or chest tightness), hot flashes, cold flashes, burning sensations (particularly in the facial or neck area), sweating, nausea, dizziness (or slight vertigo), light-headedness, hyperventilation, paresthesias (tingling sensations), sensations of choking or smothering, difficulty moving, and derealization. These physical symptoms are interpreted with alarm in people prone to panic attacks. This results in increased anxiety and forms a positive feedback loop.

Often, the onset of shortness of breath and chest pain are the predominant symptoms. People with a panic attack may incorrectly attribute them to a heart attack and thus trigger seeking treatment in an emergency room. However, since chest pain and shortness of breath are indeed hallmark symptoms of cardiovascular illnesses, including unstable angina and myocardial infarction (heart attack), especially in a person whose mental health status and heart health status are not known, attributing these pains to simple anxiety and not (also) a physical condition is a diagnosis of exclusion (other conditions must be ruled out first) until an electrocardiogram and a mental health assessment have been carried out.

Panic attacks are distinguished from other forms of anxiety by their intensity and their sudden, episodic nature. They are often experienced in conjunction with anxiety disorders and other psychological conditions, although panic attacks are not generally indicative of a mental disorder.

In an acute context, hypoxemia can cause symptoms such as those in respiratory distress. These include breathlessness, an increased rate of breathing, use of the chest and abdominal muscles to breathe, and lip pursing.

Chronic hypoxemia may be compensated or uncompensated. The compensation may cause symptoms to be overlooked initially, however, further disease or a stress such as any increase in oxygen demand may finally unmask the existing hypoxemia. In a compensated state, blood vessels supplying less-ventilated areas of the lung may selectively contract, to redirect the blood to areas of the lungs which are better ventilated. However, in a chronic context, and if the lungs are not well ventilated generally, this mechanism can result in pulmonary hypertension, overloading the right ventricle of the heart and causing cor pulmonale and right sided heart failure. Polycythemia can also occur. In children, chronic hypoxemia may manifest as delayed growth, neurological development and motor development and decreased sleep quality with frequent sleep arousals.

Other symptoms of hypoxemia may include cyanosis, digital clubbing, and symptoms that may relate to the cause of the hypoxemia, including cough and hemoptysis.

Serious hypoxemia occurs (1) when the partial pressure of oxygen in blood is less than 60 mm Hg, (the beginning of the steep portion of the oxygen–haemoglobin dissociation curve, where a small decrease in the partial pressure of oxygen results in a large decrease in the oxygen content of the blood); or (2) when hemoglobin oxygen saturation is less than 90%. Severe hypoxia can lead to respiratory failure

Generalized anxiety disorder is when our minds are troubled about some uncertain event, or in other words, when we feel threatened, although the source of the threat might not be obvious to us. It is a disorder when it happens frequently, and disables people from accomplishing some of their daily activities. Generalized anxiety disorder always comes before phobophobia, and of its symptoms are listed below:

1. Paleness of skin

2. Sweating

3. Dilation of pupils

4. Rapid pounding of heart

5. Rise in blood pressure

6. Tension in the muscles

7. Trembling

8. Readiness to be startled

9. Dryness and tightness of the throat and mouth

10. Rapid breathing

11. Desperation

12. A sinking feeling in the stomach

13. A strong desire to cry, run or hide

The main problem with this disorder is that we do not know what we are troubled about, which may lead to our desire to escape. Anxiety becomes a disorder only when we experience psychological trauma, in which our knowledge of past events trigger a fear of uncertain danger in the future. In other words, the primarily event is anxiety which arises for no accountable reason, panic might develop from anxiety and the phobophobia is developed in the very end as a consequence of both of them, sharing some of the symptoms. If either of these initiating disorders are not treated, phobophobia can be developed because an extended susceptibility and experience of this feelings can create an extreme predisposition to other phobias. Anxiety is mainly fixed to a certain specific event or specific events, a strong learned drive which is situationally evoked which is stressful to one person but not to another, and this makes it much easier for phobophobia to develop, as well as other phobias.

Dizziness is an impairment in spatial perception and stability. Because the term "dizziness" is imprecise, it can refer to vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness.

One can induce dizziness by engaging in disorientating activities such as spinning.

- Vertigo is the sensation of spinning or having one's surroundings spin about them. Many people find vertigo very disturbing and often report associated nausea and vomiting. It represents about 25% of cases of occurrences of dizziness.

- Disequilibrium is the sensation of being off balance, and is most often characterized by frequent falls in a specific direction. This condition is not often associated with nausea or vomiting.

- Presyncope is lightheadedness, muscular weakness and feeling faint as opposed to a syncope, which is actually fainting.

- Non-specific dizziness is often psychiatric in origin. It is a diagnosis of exclusion and can sometimes be brought about by hyperventilation.

A stroke is the cause of isolated dizziness in 0.7% of people who present to the emergency room.