A sudden lack of strength in the legs and inability to stand up, without sensory abnormalities or bowel or urinary dysfunction, is likely to be hypokalemic periodic paralysis. Hypokalemic periodic paralysis is a recurrent skeletal muscle flaccid paralysis caused by abnormal potassium metabolism. This condition tends to recur, so it is called periodic paresis, which does not affect the function of urination and defecation. Acute myelitis is an acute transverse inflammatory change of the spinal cord caused by an autoimmune reaction. The disease develops rapidly and often manifests as sensory disturbances in the limbs below the plane of damage and urinary and defecation disturbances. Sudden leg weakness is more common.