Numbness in the arms at night while sleeping is caused by incorrect sleep posture or due to cervical spondylosis, which can also be caused by cerebral ischemia. Incorrect sleep posture, lying on the side or having a large head tilt angle can lead to long-term pressure on one limb, which can affect the normal blood circulation process and lead to numbness in the arm. With cervical spondylosis, the protruding intervertebral disc will compress the vertebral artery or adjacent nerve roots, resulting in a gradual decrease in the amount of blood passing through the vertebral artery, which will also lead to ischemia and hypoxia in the brain, which will damage the corresponding nerve stages, thus leading to arm numbness. Cerebral ischemia produces can lead to insufficient blood and oxygen supply to the brain, and in severe cases can cause thrombosis to compress local tissues and affect normal nerve function, thus causing abnormal sensation in the limbs.