From OMIMThere are 2 dominantly inherited, clinically similar types of episodic flaccid generalized weakness, HOKPP and HYPP, that are distinguished by the changes in serum potassium levels during paralytic attacks. In contrast to HYPP, myotonia is usually not present in HOKPP (Jurkat-Rott et al., 2000). Hypokalemic periodic paralysis may also occur as a rare complication of thyrotoxicosis (see TTPP1, 188580), a disorder with a high frequency in individuals of Asian descent (Kung, 2006).
http://www.omim.org/entry/170400 From MedlinePlus GeneticsHypokalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness typically beginning in childhood or adolescence. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Attacks cause severe weakness or paralysis that usually lasts from hours to days. Some people may have episodes almost every day, while others experience them weekly, monthly, or only rarely. Attacks can occur without warning or can be triggered by factors such as rest after exercise, a viral illness, or certain medications. Often, a large, carbohydrate-rich meal or vigorous exercise in the evening can trigger an attack upon waking the following morning. Although affected individuals usually regain their muscle strength between attacks, some develop persistent muscle weakness later in life.
People with hypokalemic periodic paralysis typically have reduced levels of potassium in their blood (hypokalemia) during episodes of muscle weakness. Researchers are investigating how low potassium levels may be related to the muscle abnormalities in this condition.
https://medlineplus.gov/genetics/condition/hypokalemic-periodic-paralysis