From GeneReviews
Hyperkalemic periodic paralysis (hyperPP) is characterized by attacks of flaccid limb weakness (which may also include weakness of the muscles of the eyes, throat, breathing muscles, and trunk), hyperkalemia (serum potassium concentration >5 mmol/L) or an increase of serum potassium concentration of at least 1.5 mmol/L during an attack of weakness and/or provoking/worsening of an attack by oral potassium intake, normal serum potassium between attacks, and onset before age 20 years. In approximately half of affected individuals, attacks of flaccid muscle weakness begin in the first decade of life, with 25% reporting their first attack at age ten years or older. Initially infrequent, the attacks then increase in frequency and severity over time until approximately age 50 years, after which the frequency of attacks declines considerably. The major attack trigger is eating potassium-rich foods; other triggers include: cold environment; rest after exercise, stress, or fatigue; alcohol; hunger; and changes in activity level. A spontaneous attack commonly starts in the morning before breakfast, lasts for 15 minutes to one hour, and then passes. Individuals with hyperPP frequently have myotonia (muscle stiffness), especially around the time of an episode of weakness. Paramyotonia (muscle stiffness aggravated by cold and exercise) is present in about 45% of affected individuals. More than 80% of individuals with hyperPP older than age 40 years report permanent muscle weakness and about one third develop a chronic progressive myopathy.
From MedlinePlus GeneticsHyperkalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness or paralysis, usually beginning in infancy or early childhood. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Episodes tend to increase in frequency until mid-adulthood, after which they occur less frequently in many people with the condition. Factors that can trigger attacks include rest after exercise, potassium-rich foods such as bananas and potatoes, stress, fatigue, alcohol, pregnancy, exposure to hot or cold temperatures, certain medications, and periods without food (fasting). Muscle strength usually returns to normal between attacks, although many affected people continue to experience mild stiffness (myotonia), particularly in muscles of the face and hands.
Most people with hyperkalemic periodic paralysis have increased levels of potassium in their blood (hyperkalemia) during attacks. Hyperkalemia results when the weak or paralyzed muscles release potassium ions into the bloodstream. In other cases, attacks are associated with normal blood potassium levels (normokalemia). Ingesting potassium can trigger attacks in affected individuals, even if blood potassium levels do not go up.
https://medlineplus.gov/genetics/condition/hyperkalemic-periodic-paralysis