Acute generalized muscle weakness may have a different underlying cause. Among all urgently admitted patients, hypokalemia is observed in more than 20% of cases. Usually blood potassium concentration decrease is not fatal, but severe hypokalemia can be life-threatening for the patient suffering from cardiovascular diseases and respiratory disorders. Hypokalemia manifests clinically by muscle pain, weakness, the intestinal motility disorders, constipation, marked decrease in serum potassium levels can lead to fatal rhabdomyolysis. The key hormones that regulate the total stock of potassium in the body and its normal redistribution of intra- and extracellular fluid are insulin and catecholamines, interacting with β-adrenergic receptors. Regulation of blood potassium level is provided by insulin and it is a feedback (hyperkalemia stimulates insulin secretion, decreased potassium levels inhibits it). The level of catecholamines is not determined by potassium concentration, however, it influences the serum potassium level. Hypokalemia is usually the result of potassium loss due to abnormal renal (treatment with thiazides, high doses of corticosteroids, antibiotics, primary hyperaldosteronism due to adenoma, adrenal carcinoma, bilateral adrenal hyperplasia, Liddle, Bartter’s, Gitelman’s syndromes, 11β-hydroxysteroid dehydrogenase, 11β-hydroxylase, 17α-hydroxylase deficiency, Cushing’s syndrome) or extrarenal (intense vomiting, diarrhea due to excessive laxative use, salmonellosis, yersiniosis, HIV-infection, bowel tumors, chemotherapy, radiation therapy in cancer patients, celiac disease, jejunoileal bypass, a lack of potassium in food) potassium loss, an also a transmembrane shift of potassium (hypokalemic familial periodic paralysis, β2-agonist, bronchodilators, theophylline intake). Hypokalemic myoplegia may lead to fatal complications, requiring doctors of various specialties’ to know the clinical manifestations of hypokalemia, which may have different underlying cause.