If you wake up with numbness in your arms, it may be caused by the following conditions: 1. It may be caused by poor blood circulation in the upper limbs. Some patients are often used to overflexing their upper limbs or lying on their sides to the other side when they sleep. This will lead to some large blood vessels leading to the upper limbs being squeezed or twisted, which will cause long-term poor blood circulation in the upper limbs, and will cause the upper limbs to become very numb after the patient wakes up. The patient may have a very numb and tingling sensation in the upper limb due to the restoration of blood circulation during the process of moving the upper limb.2. It may be caused by nerve entrapment, such as the long-term entrapment of some nerve travel areas in the upper limb, resulting in numbness in the area of its distribution, which is more common when the elbow joint is under pressure. If the patient adopts a supine position, long-term pressure on the medial side of the elbow joint may lead to numbness on the ulnar side of the forearm as well as on the little finger and ring finger of the hand. 3. It may be caused by long-term pressure on the entire limb. Some patients are accustomed to sleep with their hands under their heads or press one of their upper limbs under their bodies, resulting in simultaneous pressure on blood vessels and nerves, which can cause very serious numbness and, in serious cases, necrosis of the extremity.