Arms go numb when sleeping mainly due to pressure on nerves or restricted blood flow caused by certain sleeping positions. This pressure compresses nerves or limits circulation, leading to numbness or tingling sensations commonly known as "paresthesia".
Sleeping with arms bent, under the head, or in positions that stretch or compress nerves near the wrist, elbow, or shoulder often causes this numbness. Lying on the stomach or having wrists flexed can be especially problematic.
Other underlying causes that contribute to numb arms during sleep include conditions like carpal tunnel syndrome (compression of the median nerve in the wrist), cervical spine issues (pinched nerves in the neck), thoracic outlet syndrome, vitamin deficiencies (such as B12), and nerve damage from injuries or diseases.
If numbness occurs frequently, persists after changing positions, or is associated with pain or weakness, it may indicate a medical condition requiring evaluation by a healthcare professional.
In summary, most commonly, arm numbness when sleeping results from nerve compression or poor blood flow due to sleeping posture, but sometimes it points to underlying nerve or health issues that need attention.