Numbness of the arm when sleeping flat on the ground may be caused by cervical spondylosis, osteoarthrosis, insufficient blood supply to the brain and other reasons. 1. Cervical spondylosis: patients with cervical spondylosis such as radiculopathy, cervical disc herniation, cervical spine degeneration or hyperplasia, which will cause compression of the cervical nerve root, and the symptom of numbness of the arm lying down in bed will occur. 2. Osteoarthropathy: the degeneration of the articular cartilage in the arm area leads to nerve damage around the joints, and the proliferation of bone may irritate the nerves when you lie down to sleep, resulting in numbness in the arm when you lie down to sleep. 3. Insufficient blood supply to the brain: patients with insufficient blood supply to the brain may also experience numbness in the arm when sleeping flat on their backs, which may be accompanied by other symptoms such as headache, dizziness and blurred vision. If the numbness of the arm lying on the floor can not be relieved for a long time or the symptoms are aggravated, it is recommended that the patient go to the hospital to find out the cause of the disease and carry out targeted treatment.