Attacks of intermittent weakness that do not begin until adulthood are rare and usually caused by other disorders. The frequency of attacks varies from daily to yearly. Episodes of muscle weakness may last for a few hours or persist for several days. Serum potassium levels are normal between attacks. There is no decrease in total body potassium, however.
Potassium flows from the bloodstream into muscle cells.
Insulin levels may affect the disorder in some people because insulin increases the flow of potassium into cells. Although muscle strength is initially normal between attacks, repeated attacks may eventually cause progressive and persistent muscle weakness between attacks. Risks include a family history of periodic paralysis. Attacks may be triggered by ingestion of high carbohydrate meals. Attacks most commonly occur after sleep or rest and are rare during exercise , but rest after an exercise period may trigger an attack.