Rare autosomal dominant neuromuscular disorder typically found in adolescent males (due to mutations of CACNA1s and SCN4A). Characterized by episodes of painless muscle weakness precipitated by heavy exercise, fasting, or high-carbohydrate meals.

This paralysis, unlike hyperkalemic periodic paralysis, is associated with low potassium levels (<2.4 mEq/L; <2 suggests a secondary cause of hypokalemia). Established familial history is diagnostic.