If you experience numbness in your arms at night while sleeping, it may be caused by several reasons: First, it may be caused by a jammed blood vessel in the upper extremity. This condition can be either physiological or pathological. The physiological situation is common when the patient takes a lateral posture, and when lying on the side, the neck and shoulder, the upper limbs have a particularly serious case of compression or bending, which will lead to the important blood vessels to the upper limbs are squeezed or bent, resulting in insufficient blood supply to the upper limbs, after which the upper limbs will produce cold, numbness, many patients have a similar experience. Once the posture is changed after this condition and the blood circulation in the upper extremity is restored, more severe tingling will occur in the extremity, followed by tingling before it slowly subsides. The pathological condition is the presence of thoracic outlet syndrome, which occurs when sleeping on the side due to bony or muscular hyperplasia in the thoracic area, causing the blood vessels in the upper limbs to become stuck. Second, the presence of peripheral neuropathy, such as the presence of cervical spondylosis, there is a possibility of numbness in the upper limbs during sleep. If the upper limb is not placed properly, resulting in compression of certain peripheral nerves in the upper limb, it can also produce this symptom, most commonly the ulnar nerve is compressed in the ulnar nerve groove position, that is, the elbow position is compressed, producing numbness in the inner part of the upper limb.