In the early stages, it can be difficult to distinguish progressive myoclonic epilepsy from benign idiopathic generalised epilepsies, such as juvenile myoclonic epilepsy. With PME, the initial effectiveness of anticonvulsant treatment diminishes as seizures become more frequent and neurological decline progresses. However, these can also be signs of anticonvulsant intoxication. The myoclonus in PME is usually severe and is the prominent seizure type.

Myoclonic seizures involve brief involuntary muscle twitching, and may become frequent enough to be disabling. Tonic-clonic seizures have two phases: the tonic phase may last a few seconds and involves the muscles tensing, and may lead to the person falling down; the clonic phase involves a convulsion of rapidly alternating muscle tensing and relaxing. Neurological dysfunction includes difficulty coordinating muscle movements (ataxia) and a decline in cognitive ability (dementia).

Patients with Unverricht–Lundborg disease exhibit myoclonic jerks and tonic-clonic seizures at a young age, between ages 6–16. The myoclonic jerks occur in the muscles of the arms and legs closest to the torso, and are triggered due to a variety of common external stimuli. Seizures begin at an average age of 10.8 years, with myoclonus beginning around 12.1 years. It is not currently possible to diagnose without a genetic test, and since early symptoms are general, it is often mistaken for another more common epilepsy, in many cases juvenile myoclonic epilepsy (JME).

Myoclonic jerks that are not epileptic may be due to a nervous system disorder or other metabolic abnormalities that may arise in renal (e.g. hyperuraemia) and liver failure (e.g. high ammonia states).

The most common type (60%) of seizures are convulsive. Of these, one-third begin as generalized seizures from the start, affecting both hemispheres of the brain. Two-thirds begin as focal seizures (which affect one hemisphere of the brain) which may then progress to generalized seizures. The remaining 40% of seizures are non-convulsive. An example of this type is the absence seizure, which presents as a decreased level of consciousness and usually lasts about 10 seconds.

Focal seizures are often preceded by certain experiences, known as auras. They include sensory (visual, hearing, or smell), psychic, autonomic, and motor phenomena. Jerking activity may start in a specific muscle group and spread to surrounding muscle groups in which case it is known as a Jacksonian march. Automatisms may occur, which are non-consciously-generated activities and mostly simple repetitive movements like smacking of the lips or more complex activities such as attempts to pick up something.

There are six main types of generalized seizures: tonic-clonic, tonic, clonic, myoclonic, absence, and atonic seizures. They all involve loss of consciousness and typically happen without warning.

Tonic-clonic seizures occur with a contraction of the limbs followed by their extension along with arching of the back which lasts 10–30 seconds (the tonic phase). A cry may be heard due to contraction of the chest muscles, followed by a shaking of the limbs in unison (clonic phase). Tonic seizures produce constant contractions of the muscles. A person often turns blue as breathing is stopped. In clonic seizures there is shaking of the limbs in unison. After the shaking has stopped it may take 10–30 minutes for the person to return to normal; this period is called the "postictal state" or "postictal phase." Loss of bowel or bladder control may occur during a seizure. The tongue may be bitten at either the tip or on the sides during a seizure. In tonic-clonic seizure, bites to the sides are more common. Tongue bites are also relatively common in psychogenic non-epileptic seizures.

Myoclonic seizures involve spasms of muscles in either a few areas or all over. Absence seizures can be subtle with only a slight turn of the head or eye blinking. The person does not fall over and returns to normal right after it ends. Atonic seizures involve the loss of muscle activity for greater than one second. This typically occurs on both sides of the body.

About 6% of those with epilepsy have seizures that are often triggered by specific events and are known as reflex seizures. Those with reflex epilepsy have seizures that are only triggered by specific stimuli. Common triggers include flashing lights and sudden noises. In certain types of epilepsy, seizures happen more often during sleep, and in other types they occur almost only when sleeping.

Progressive myoclonus epilepsy is a disease associated with myoclonus, epileptic seizures, and other problems with walking or speaking. These symptoms often worsen over time and can be fatal.

MERRF syndrome is also known as myoclonic epilepsy with ragged-red fibers. This rare inherited disorder affects muscles cells. Features of MERRF, along with myoclonus epilepsy seizures, include ataxia, peripheral neuropathy, and dementia.

Lafora disease is also known as Lafora progressive myoclonus epilepsy, which is an autosomal recessive inherited disorder involving recurrent seizures and degradation of mental capabilities. Lafora disease usually occurs in late childhood and usually leads to death around 10 years after first signs of the disease.

Unverricht-Lundborg disease is an autosomal recessive inherited disorder seen in individuals as young as six years. It is associated with possible loss of consciousness, rigidity, ataxia, dysarthria, declination of mental functioning, and involuntary shaking.

Neuronal ceroid lipofuscinosis is a group of diseases that cause blindness, loss of mental abilities, and loss of movement. All diseases in this group are lysosomal-storage disorders that also lead to death roughly ten years after onset of the disease.

Juvenile myoclonic epilepsy (JME) is an idiopathic generalized epilepsy that occurs in patients aged 8 to 20 years. Patients have normal cognition and are otherwise neurologically intact. The most common seizure is myoclonic jerks, although generalized tonic-clonic seizures and absence seizures may occur as well. Myoclonic jerks usually cluster in the early morning after awakening. The EEG reveals generalized 4–6 Hz spike wave discharges or multiple spike discharges. These patients are often first diagnosed when they have their first generalized tonic-clonic seizure later in life, when they experience sleep deprivation (e.g., freshman year in college after staying up late to study for exams). Alcohol withdrawal can also be a major contributing factor in breakthrough seizures, as well. The risk of the tendency to have seizures is lifelong; however, the majority have well-controlled seizures with anticonvulsant medication and avoidance of seizure precipitants.

Frontal lobe epilepsy, usually a symptomatic or cryptogenic localization-related epilepsy, arises from lesions causing seizures that occur in the frontal lobes of the brain. These epilepsies can be difficult to diagnose because the symptoms of seizures can easily be confused with nonepileptic spells and, because of limitations of the EEG, be difficult to "see" with standard scalp EEG.

Juvenile absence epilepsy is an idiopathic generalized epilepsy with later onset than CAE, typically in prepubertal adolescence, with the most frequent seizure type being absence seizures. Generalized tonic-clonic seizures can occur. Often, 3 Hz spike-wave or multiple spike discharges can be seen on EEG. The prognosis is mixed, with some patients going on to a syndrome that is poorly distinguishable from JME.

After the active portion of a seizure (the ictal state) there is typically a period of recovery during which there is confusion, referred to as the postictal period before a normal level of consciousness returns. It usually lasts 3 to 15 minutes but may last for hours. Other common symptoms include feeling tired, headache, difficulty speaking, and abnormal behavior. Psychosis after a seizure is relatively common, occurring in 6–10% of people. Often people do not remember what happened during this time. Localized weakness, known as Todd's paralysis, may also occur after a focal seizure. When it occurs it typically lasts for seconds to minutes but may rarely last for a day or two.

Originally called Doose syndrome, epilepsy with myoclonic-astatic seizures accounts for ~2% of childhood epilepsies. Children with this disorder have incredibly brief (<100ms) myoclonic jerks followed by equally brief loss of muscle tone, sometimes resulting in dangerous falls. Some patients have much longer lasting seizures of this type. Many patients with this disorder also have absence seizures. This is believed to be a polygenic disorder.

The hallmark characteristic of PCDH19 gene-related epilepsy is early-onset cluster seizures that often cause cyanotic spells, which start in infancy or early childhood. The onset of the first cluster of seizures usually coincides with a fever (febrile seizures), however subsequent seizures may be febrile or afebrile. The seizure clusters are generally brief seizures, lasting 1–5 minutes, often accompanied by fearful screaming observed in 63% of girls. These cluster seizures can occur more than 10 times a day over several days, with varying amounts of time between seizure clusters.

Over time, children with PCDH19 gene-related epilepsy tend to exhibit multiple seizure types, including focal, generalized tonic-clonic, tonic, atonic, myclonus, and absence seizures. In a small study of 35 female patients with PCDH19 gene-related epilepsy, rare episodes of status epilepticus occurred in about 30% of patients in the early course of the disorder.

In PCDH19 gene-related epilepsy, the seizures are often refractory to treatment, especially in infancy and childhood. Additionally, seizures are usually characterized by persistence of cluster seizures, with variable frequency. In a study of 35 female patients with PCDH19 gene-related epilepsy, approximately 30% had become seizure free in the girl's childhood (mean age of 12 years), yet some continued into adulthood. In the same study, a few patients still had recurrent cluster seizures that evolved into status epilepticus in childhood or early adolescence.

The genetic cause of ULD is known, but research has led to new areas of study that may lead to an increase in knowledge of what causes ULD.

Northern Epilepsy Syndrome causes recurrent seizures between the ages of five to ten. These seizures, that may last up to 15 minutes, can be classified mostly as tonic-clonic, but partial seizures could also occur. The seizures commonly involve muscle rigidity, convulsions, and loss of consciousness. Generally, the recurrence is one to two times per month.

In the years following the onset of seizures, a noticeable decrease in intellectual capacity is observed.

This rare epilepsy has a wide age range of presentation (from the first year of life through the early teens). This epilepsy is characterized by absence seizures concurrent with myoclonic jerks, typically occurring several times daily. The genetics of this disorder have not been delineated. Seizures from this disorder often cease within 5 years.

During puberty, seizure frequency increases to one to two times per week. Mental function has a rapid decline, as observed by a lack of coordination, failure to complete education, and fine motor activities. In rare cases, some suffered from loss of vision.

Signs of JME are brief episodes of involuntary muscle twitching occurring early in the morning or shortly before falling asleep. This does not usually result in the person falling, but rather dropping objects. These muscle twitching episodes are more common in the arms than in the legs. Other seizure types such as generalized tonic-clonic and absence seizures can also occur. Patients often report quick jerking movements in the morning that results in knocking over objects such as their morning orange juice. Clusters of myoclonic seizures can lead to absence seizures, and clusters of absence seizures can lead to generalized tonic-clonic seizures. The onset of symptoms is generally around age 10-16 although some patients can present in their 20s or even early 30s. The myoclonic jerks generally precede the generalized tonic-clonic seizures by several months. Some people with the disorder never get generalized tonic-clonic seizures (GTCs). Sleep deprivation is a major factor in triggering GTCs. College students often present with a GTC after "pulling an all-nighter." Patients with JME generally do not have other neurological problems.

Dravet syndrome has been characterized by prolonged febrile and non-febrile seizures within the first year of a child’s life. This disease progresses to other seizure types like myoclonic and partial seizures, psychomotor delay, and ataxia. It is characterized by cognitive impairment, behavioral disorders, and motor deficits. Behavioral deficits often include hyperactivity and impulsiveness, and in more rare cases, autistic-like behaviors. Dravet syndrome is also associated with sleep disorders including somnolence and insomnia. The seizures experienced by people with Dravet syndrome become worse as the patient ages since the disease is not very predictable when first diagnosed. This coupled with the range of severity differing between each individual diagnosed and the resistance of these seizures to drugs has made it challenging to develop treatments.

Dravet syndrome appears during the first year of life, often beginning around six months of age with frequent febrile seizures (fever-related seizures). Children with Dravet syndrome typically experience a lagged development of language and motor skills, hyperactivity and sleep difficulties, chronic infection, growth and balance issues, and difficulty relating to others. The effects of this disorder do not diminish over time, and children diagnosed with Dravet syndrome require fully committed caretakers with tremendous patience and the ability to closely monitor them.

Febrile seizures are divided into two categories known as simple and complex. A febrile seizure would be categorized as complex if it has occurred within 24 hours of another seizure or if it lasts longer than 15 minutes. A febrile seizure lasting less than 15 minutes would be considered simple. Sometimes modest hyperthermic stressors like physical exertion or a hot bath can provoke seizures in affected individuals. However, any seizure uninterrupted after 5 minutes, without a resumption of postictal (more normal; recovery-type; after-seizure) consciousness can lead to potentially fatal status epilepticus.

Tonic–clonic Seizures with repetitive sequences of stiffening and jerking of the extremities.

Myoclonic Seizures with rapid, brief contractions of muscles.

Atonic Seizures with a sudden loss of muscle tone, often resulting in sudden collapse. These are also called drop seizures.

Absence A generalized seizure characterized by staring off and occasionally some orofacial automatisms.

Myoclonic astatic Seizures that involve a myoclonic seizure followed immediately by an atonic seizure. This type of seizure is exclusive to MAE and is one of the defining characteristics of this syndrome.

Tonic Muscle stiffening or rigidity. This seizure is rare in this syndrome.

A seizure can last from a few seconds to more than five minutes, at which point it is known as status epilepticus. Most tonic-clonic seizures last less than two or three minutes. Absence seizures are usually around 10 seconds in duration.

There are six main types of generalized seizures: tonic-clonic, tonic, clonic, myoclonic, absence, and atonic seizures. They all involve a loss of consciousness and typically happen without warning.

- Tonic-clonic seizures present with a contraction of the limbs followed by their extension, along with arching of the back for 10–30 seconds. A cry may be heard due to contraction of the chest muscles. The limbs then begin to shake in unison. After the shaking has stopped it may take 10–30 minutes for the person to return to normal.

- Tonic seizures produce constant contractions of the muscles. The person may turn blue if breathing is impaired.

- Clonic seizures involve shaking of the limbs in unison.

- Myoclonic seizures involve spasms of muscles in either a few areas or generalized through the body.

- Absence seizures can be subtle, with only a slight turn of the head or eye blinking. The person often does not fall over and may return to normal right after the seizure ends, though there may also be a period of post-ictal disorientation.

- Atonic seizures involve the loss of muscle activity for greater than one second. This typically occurs bilaterally (on both sides of the body).

Epilepsy is most commonly recognised by involuntary movements of the head and limbs, however other characteristics include salivation, lack of and anxiety. Animals often lose consciousness and are not aware of their surroundings.

Beyond early-onset and treatment-resistant cluster seizures, PCDH19 gene-related epilepsy is usually, but not always, associated with cognitive and sensory impairment of varying degrees, and psychiatric and behavioral problems. It is estimated that up to 60 to 75% of the females have cognitive deficits, ranging from mild to severe intellectual disability, which do not appear to be related to frequency or severity of seizures. Development over the course of a female patients’ childhood can follow one of three courses: delays from birth that persist into adulthood, normal development and then regression, or normal intellectual development. It is not yet clear why some people experience delayed intellectual growth and others regress with epilepsy.

From the University of Melbourne study, two-thirds of PCDH19 gene-related epilepsy patients have borderline intellectual functioning or intellectual disability, while one third have normal intelligence. A connection to depression, autism, obsessive and aggressive behaviors and other disorders has been observed in PCDH19 gene-related epilepsy. Approximately 40-60% of girls diagnosed with a PCDH19 mutation are on the autism spectrum.

Many of those with PCDH19 gene mutations also exhibit behavioral and psychological problems – including ADHD, aggression, obsessive-compulsive disorder, and anxiety. Other neurological abnormalities may present, including sleep disturbances, ictal apnea, motor deficits, hypotonia, language delay, sensory integration problems and dysautonomia.

The onset of seizures is between the ages of 2 and 5. EEG shows regular and irregular bilaterally synchronous 2- to 3-Hz spike-waves and polyspike patterns with a 4- to 7-Hz background. 84% of affected children show normal development prior to seizures; the remainder show moderate psychomotor retardation mainly affecting speech. Boys (74%) are more often affected than girls (Doose and Baier 1987a).

The age of onset of seizures is typically between three and five, though onset can occur at an earlier or later age. The syndrome shows clear parallels to West syndrome, enough to suggest a connection.

Daily multiple seizures are typical in LGS. Also typical is the broad range of seizures that can occur, larger than that of any other epileptic syndrome. The most frequently occurring seizure type is tonic seizures, which are often nocturnal (90%); the second most frequent are myoclonic seizures, which often occur when the person is over-tired.

Atonic, atypical absence, tonic, complex partial, focalized and tonic–clonic seizures are also common. Additionally, about half of patients will have status epilepticus, usually the nonconvulsive type, which is characterized by dizziness, apathy, and unresponsiveness. The seizures can cause sudden falling (or spasms in tonic, atonic and myoclonic episodes) and/or loss of balance, which is why patients often wear a helmet to prevent head injury.

In addition to daily multiple seizures of various types, children with LGS frequently have arrested/slowed psycho-motor development and behavior disorders.

The syndrome is also characterized by an (between-seizures) EEG featuring slow spike-wave complexes.

Watching an animal have a seizure can be quite frightening. There is not much that can be done during a seizure except to remain calm and not leave the animal alone. If your pet is having a seizure it is important to make sure they are laying down on the floor away from any water, stairs or other animals. When an animal has a seizure, do not try to grab their tongue or clear their mouth as there is a high chance you will be bitten; contrary to popular myth, neither humans nor animals can "swallow their tongue" during a seizure so it is safest to stay well away from their mouth during one. Timing seizures is also crucial. Take notes of seizures - what time they occur, how often and any other specific information which can be passed onto the vet or emergency animal clinic.