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.

Treatment for lightheadedness depends on the cause or underlying problem. Treatment may include drinking plenty of water or other fluids (unless the lightheadedness is the result of water intoxication in which case drinking water is quite dangerous). If a sufferer is unable to keep fluids down from nausea or vomiting, they may need intravenous fluid. Sufferers should try eating something sugary and lying down or sitting and reducing the elevation of the head relative to the body (for example, by positioning the head between the knees).

Other simple remedies include avoiding sudden changes in posture when sitting or lying and avoiding bright lights.

Several essential electrolytes are excreted when the body perspires. When people are out in unusual or extreme heat for a long time, sweating excessively can cause a lack of some electrolytes, which in turn can cause lightheadedness.

Many conditions cause dizziness because multiple parts of the body are required for maintaining balance including the inner ear, eyes, muscles, skeleton, and the nervous system.

Common physiological causes of dizziness include:

- inadequate blood supply to the brain due to:

- a sudden fall in blood pressure

- heart problems or artery blockages

- loss or distortion of vision or visual cues

- disorders of the inner ear

- distortion of brain/nervous function by medications such as anticonvulsants and sedatives

- result of side effect from prescription drugs, including proton-pump inhibitor drugs (PPIs) and Coumadin (warfarin) causing dizziness/fainting

Dizziness is broken down into 4 main subtypes: vertigo (~50%), disequilibrium (less than ~15%), presyncope (less than ~15%) and lightheadedness (~10%).

Orthostatic hypotension may be caused by low blood volume, resulting from bleeding, the excessive use of diuretics, vasodilators, or other types of drugs, dehydration, or prolonged bed rest(immobility); as well as occurring in people with anemia.

Orthostatic hypotension may cause accidental falls. It is also linked to an increased risk of cardiovascular disease, heart failure, and stroke. There is also observational data suggesting that orthostatic hypotension in middle age increases the risk of eventual dementia and reduced cognitive function.

The tilt table test is an evaluative clinical test to help identify postural hypotension, a common cause of presyncope or syncope. A tilt angle of 60 and 70 degrees is optimal and maintains a high degree of specificity. A positive sign with the tilt table test must be taken in context of patient history, with consideration of pertinent clinical findings before coming to a conclusion.

Presyncope is a state of lightheadedness, muscular weakness, blurred vision, and feeling faint (as opposed to a syncope, which is actually fainting). Presyncope is most often cardiovascular in cause. In many people, lightheadedness is a symptom of orthostatic hypotension. Orthostatic hypotension occurs when blood pressure drops significantly when the patient stands from a supine (horizontal) or seatted position. If loss of consciousness occurs in this situation, it is termed syncope.

Presyncope is frequently reported in people with autonomic dysfunctions such as the postural orthostatic tachycardia syndrome (POTS).

The prevalence of POTS is unknown. One study estimated a minimal rate of 170 POTS cases per 100,000 individuals, but the true prevalence is likely higher due to underdiagnosis. Another study estimated that there were between 500,000 and 3,000,000 cases in the United States. POTS is more common in women, with a female-to-male ratio of 5:1. Most people with POTS are aged between 20 and 40, with an average onset of 30. Diagnoses of POTS beyond age 40 are rare, perhaps because symptoms improve with age.

Symptoms of OI are triggered by the following:

- An upright posture for long periods of time (e.g. standing in line, standing in a shower, or even sitting at a desk).

- A warm environment (such as in hot summer weather, a hot crowded room, a hot shower or bath, after exercise).

- Emotionally stressful events (seeing blood or gory scenes, being scared or anxious).

- Astronauts returning from space not yet re-adapted to gravity.

- Extended bedrest

- Inadequate fluid and salt intake.

Brief periods of unconsciousness do no harm and are seldom symptoms of disease.

The main danger of vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious. Medication therapy could possibly prevent future vasovagal responses; however, for some individuals medication is ineffective and they will continue to have fainting episodes.

POTS has a favorable prognosis when managed appropriately. Symptoms improve within five years of diagnosis for many patients, and 60% return to their original level of functioning. About 90% of people with POTS respond to a combination of pharmacological and physical treatments. Those who develop POTS in their early to mid teens during a period of rapid growth will most likely see complete symptom resolution in two to five years. Outcomes are more guarded for adults newly diagnosed with POTS. Some people do not recover, and a few even worsen with time. The hyperadrenergic type of POTS typically requires continuous therapy. If POTS is caused by another condition, outcomes depend on the prognosis of the underlying disorder.

Low blood pressure can be caused by low blood volume, hormonal changes, widening of blood vessels, medicine side effects, anemia, heart problems or endocrine problems.

Reduced blood volume, hypovolemia, is the most common cause of hypotension. This can result from hemorrhage; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia is often induced by excessive use of diuretics. Low blood pressure may also be attributed to heat stroke. The body may have enough fluid but does not retain electrolytes. Absence of perspiration, light headedness and dark coloured urine are also indicators.

Other medications can produce hypotension by different mechanisms. Chronic use of alpha blockers or beta blockers can lead to hypotension. Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle.

Decreased cardiac output despite normal blood volume, due to severe congestive heart failure, large myocardial infarction, heart valve problems, or extremely low heart rate (bradycardia), often produces hypotension and can rapidly progress to cardiogenic shock. Arrhythmias often result in hypotension by this mechanism.

Some heart conditions can lead to low blood pressure, including extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure. These conditions may cause low blood pressure because they prevent the body from being able to circulate enough blood.

Excessive vasodilation, or insufficient constriction of the resistance blood vessels (mostly arterioles), causes hypotension. This can be due to decreased sympathetic nervous system output or to increased parasympathetic activity occurring as a consequence of injury to the brain or spinal cord or of dysautonomia, an intrinsic abnormality in autonomic system functioning. Excessive vasodilation can also result from sepsis, acidosis, or medications, such as nitrate preparations, calcium channel blockers, or AT1 receptor antagonists (Angiotensin II acts on AT1 receptors). Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents, produce significant vasodilation.

Meditation, yoga, or other mental-physiological disciplines may reduce hypotensive effects.

Lower blood pressure is a side effect of certain herbal medicines, which can also interact with hypotensive medications. An example is the theobromine in "Theobroma cacao", which lowers blood pressure through its actions as both a vasodilator and a diuretic, and has been used to treat high blood pressure.

Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. The nucleus tractus solitarii of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone.

This results in a spectrum of hemodynamic responses:

1. On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative chronotropic effect) and in contractility (negative inotropic effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in parasympathetic tone.

2. On the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to dilation of the blood vessels, probably as a result of withdrawal of sympathetic nervous system tone.

3. The majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.

One account for these physiological responses is the Bezold-Jarisch reflex.

Vasovagal syncope may be an evolution response, specifically the fight-or-flight response.

Orthostatic hypotension, also called "postural hypotension", is a common form of low blood pressure. It occurs after a change in body position, typically when a person stands up from either a seated or lying position. It is usually transient and represents a delay in the normal compensatory ability of the autonomic nervous system. It is commonly seen in hypovolemia and as a result of various medications. In addition to blood pressure-lowering medications, many psychiatric medications, in particular antidepressants, can have this side effect. Simple blood pressure and heart rate measurements while lying, seated, and standing (with a two-minute delay in between each position change) can confirm the presence of orthostatic hypotension. Orthostatic hypotension is indicated if there is a drop in 20 mmHg of systolic pressure (and a 10 mmHg drop in diastolic pressure in some facilities) and a 20 beats per minute increase in heart rate.

Vasovagal syncope is a form of dysautonomia characterized by an inappropriate drop in blood pressure while in the upright position. Vasovagal syncope occurs as a result of increased activity of the vagus nerve, the mainstay of the parasympathetic nervous system .

Another, but rarer form, is postprandial hypotension, a drastic decline in blood pressure that occurs 30 to 75 minutes after eating substantial meals. When a great deal of blood is diverted to the intestines (a kind of "splanchnic blood pooling") to facilitate digestion and absorption, the body must increase cardiac output and peripheral vasoconstriction to maintain enough blood pressure to perfuse vital organs, such as the brain. Postprandial hypotension is believed to be caused by the autonomic nervous system not compensating appropriately, because of aging or a specific disorder.

Hypotension is a feature of Flammer syndrome which is characterized by cold hands and feet and predisposes to normal tension glaucoma.

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.

The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope. The slow heart rate may also lead to atrial, junctional, or ventricular ectopic rhythms.

Bradycardia is not necessarily problematic. People who regularly practice sports may have sinus bradycardia, because their trained hearts can pump enough blood in each contraction to allow a low resting heart rate. Sinus bradycardia can also be an adaptive advantage; for example, diving seals may have a heart rate as low as 12 beats per minute, helping them to conserve oxygen during long dives.

Sinus bradycardia is a common condition found in both healthy individuals and those who are considered well conditioned athletes.

Heart rates considered bradycardic vary by species; for example, in the common housecat, a rate of under 120 beats per minute is abnormal. Generally, smaller species have higher heart rates while larger species have lower rates.

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.

All ethnic groups and income levels are susceptible to the illness. The CDC states that CFS is "at least as common" in African Americans and Hispanics as Caucasians. A 2009 meta-analysis, however, showed that compared with the White American majority, African Americans and Native Americans have a higher risk of CFS, though it acknowledged that studies and data were limited. More women than men get CFS — between 60 and 85% of cases are women; however, there is some indication that the prevalence among men is underreported. The illness is reported to occur more frequently in persons between the ages of 40 and 59. CFS is less prevalent among children and adolescents than among adults.

Blood relatives of those who have CFS appear to be more predisposed. There is no direct evidence that CFS is contagious.

Psychological stress, childhood trauma, perfectionist personalities, old age, lower middle education, low physical fitness, preexisting psychological illness, and allergies may be risk factors for developing chronic fatigue syndrome. This has led some to believe that stress-related visceral responses underlie CFS. Pre-existing depressive and anxiety disorders, as well as high expectation of parents and family history were predisposing factors identified in another review.

People with CFS and their relatives tend to attribute their illness to physical causes (such as a virus or pollution) rather than to psychological causes. Such attributions are associated with increased symptoms and impairment, and worse outcomes over time.

The following is a list of factors associated with an increased tendency towards developing torsades de pointes:

- Hypokalemia (low blood potassium)

- Hypomagnesemia (low blood magnesium)

- Hypocalcemia (low blood calcium)

- Bradycardia (slow heartbeat)

- Heart failure

- Left ventricular hypertrophy

- Hypothermia

- Subarachnoid hemorrhage

- Hypothyroidism

In Europe about 3% of the population has a panic attack in a given year while in the United States they affect about 11%. They are more common in females than males. They often begin during puberty or early adulthood. Children and older people are less commonly affected.

Knowledge that TdP may occur in patients taking certain prescription drugs has been both a major liability and reason for retirement of these medications from the marketplace. Examples of compounds linked to clinical observations of TdP include amiodarone, fluoroquinolones, methadone, lithium, chloroquine, erythromycin, amphetamine, ephedrine, pseudoephedrine, methylphenidate, and phenothiazines. It has also been shown as a side effect of certain anti-arrhythmic medications, such as sotalol, procainamide, and quinidine. The gastrokinetic drug cisapride (Propulsid) was withdrawn from the US market in 2000 after it was linked to deaths caused by long QT syndrome-induced torsades de pointes. In many cases, this effect can be directly linked to QT prolongation mediated predominantly by inhibition of the hERG channel.

In September 2011 (subsequently updated in March 2012 and February 2013), the FDA issued a warning concerning increased incidence of QT prolongation in patients prescribed doses of the antidepressant Celexa (citalopram) above 40 mg per day, considered the maximum allowable dosage, thereby increasing the risk of Torsades. However, a study, "Evaluation of the FDA Warning Against Prescribing Citalopram at Doses Exceeding 40 mg," reported no increased risk of abnormal arrhythmias, thus questioning the validity of the FDA's warning.

Arrhythmia may be classified by rate (tachycardia, bradycardia), mechanism (automaticity, re-entry, triggered) or duration (isolated premature beats; couplets; runs, that is 3 or more beats; non-sustained= less than 30 seconds or sustained= over 30 seconds).

It is also appropriate to classify by site of origin:

ECG characteristics

- Rate: Less than 60 beats per minute.

- Rhythm: Regular.

- P waves: Upright, consistent, and normal in morphology and duration.

- P-R Interval: Between 0.12 and 0.20 seconds in duration.

- QRS Complex: Less than 0.12 seconds in width, and consistent in morphology.

The term cardiac arrhythmia covers a very large number of very different conditions.

The most common symptom of an arrhythmia is an awareness of an abnormal heartbeat, called palpitations. These may be infrequent, frequent, or continuous. Some of these arrhythmias are harmless (though distracting for patients) but some of them predispose to adverse outcomes.

Some arrhythmias do not cause symptoms, and are not associated with increased mortality. However, some asymptomatic arrhythmias "are" associated with adverse events. Examples include a higher risk of blood clotting within the heart and a higher risk of insufficient blood being transported to the heart because of weak heartbeat. Other increased risks are of embolisation and stroke, heart failure and sudden cardiac death.

If an arrhythmia results in a heartbeat that is too fast, too slow or too weak to supply the body's needs, this manifests as a lower blood pressure and may cause lightheadedness or dizziness, or syncope (fainting).

Some types of arrhythmia result in cardiac arrest, or sudden death.

Medical assessment of the abnormality using an electrocardiogram is one way to diagnose and assess the risk of any given arrhythmia.