Sudden anal pain while sleeping may be caused by local sphincter spasm, acute inflammatory perianal infection, thrombosed external hemorrhoids and other reasons. 1. Local sphincter spasm: patients with local sphincter spasm may have severe pain, and local sphincter spasm is usually caused by anal fissure. 2. Acute perianal inflammation and infection: Acute perianal inflammation may be caused by bacterial infection, and patients may experience symptoms such as itching, pain, and increased secretion. 3. Thrombosed external hemorrhoids: Thrombosed external hemorrhoids may be caused by frequent poor bowel habits, poor dietary habits and other reasons. Patients may experience severe pain, restricted movement, anal lumps and other symptoms. It is recommended that patients go to the hospital for diagnosis and treatment in time, and do not use medication privately, so as not to cause adverse reactions.