From OMIM
Episodic ataxia is a neurologic condition characterized by spells of incoordination and imbalance, often associated with progressive ataxia (Jen et al., 2007). Genetic Heterogeneity of Episodic Ataxia Episodic ataxia is a genetically heterogeneous disorder. See also EA2 (108500), caused by mutation in the CACNA1A gene (601011) on chromosome 19p13; EA3 (606554), which maps to chromosome 1q42; EA4 (606552); EA5, caused by mutation in the CACNB4 gene (601949) on chromosome 2q22-q23; EA6 (612656), caused by mutation in the SLC1A3 gene (600111) on chromosome 5p13; EA7 (611907), which maps to chromosome 19q13; EA8 (616055), which maps to chromosome 1p36-p34; and EA9 (618924), caused by mutation in the SCN2A gene (182390) on chromosome 2q24. Isolated myokymia-2 (see 121200) is associated with mutation in the KCNQ2 gene (602235).  http://www.omim.org/entry/160120

From MedlinePlus Genetics
Episodic ataxia is a group of related conditions that affect the nervous system and cause problems with movement and coordination. People with episodic ataxia have episodes of poor coordination and balance (ataxia). During these episodes, many people also experience dizziness (vertigo), nausea and vomiting, migraines, blurred or double vision, slurred speech, and ringing in the ears (tinnitus). Seizures, muscle weakness, and paralysis that affect one side of the body (hemiplegia) may also occur during these episodes. 

Additionally, a muscle abnormality called myokymia or an eye abnormality called nystagmus can occur during or between episodes. Myokymia causes muscle cramping; stiffness; or continuous, fine muscle twitching that appears as rippling under the skin. Nystagmus refers to rapid, involuntary eye movements.

Episodes of ataxia and other symptoms can begin anytime from early childhood to adulthood. They can be triggered by environmental factors such as stress, caffeine, alcohol, certain medications, physical activity, and illness. The duration of episodes may vary from seconds to days, and the frequency ranges from several episodes per day to one or two every few months. Between episodes, affected individuals may have no signs or symptoms. However, some continue to experience ataxia, which may worsen over time.

Some children with episodic ataxia have delayed development of speech or motor skills, such as standing and walking. They may also have learning difficulties.

Researchers have identified at least 11 types of episodic ataxia, distinguished by their pattern of signs and symptoms, age of onset, length of episodes, and genetic cause.  https://medlineplus.gov/genetics/condition/episodic-ataxia