If you feel pain in your arm after waking up, there are usually several factors as follows: First, the cervical discs in the 2nd-7th vertebrae of the cervical spine are compressed during sleep, resulting in cervical protrusion and expansion of the cervical joints, and compression of the nerves that govern the upper limbs, thus causing clinical symptoms and manifestations such as arm pain after waking up. Secondly, if you exercise too much before going to bed or the muscles of the upper limbs, such as biceps and triceps, are over-exercised, it will lead to a large amount of lactic acid accumulation in the skeletal muscle, especially when waking up, which will cause excessive decomposition of lactic acid acidic metabolites, so arm pain will occur. Thirdly, if rhabdomyolysis occurs when the way and method of exercise is incorrect, or if rhabdomyolysis occurs when taking too much medication or taking the wrong medication, there will also be obvious pain in the arms when waking up. Fourth, if a disease is contracted before bedtime, such as peripheral neuritis or radiculitis, pain in the arm will also occur when waking up.