Having restless arms at night is actually a symptom of Restless Leg Syndrome, according to JAMA Neurology. As of 2015, doctors don't know the direct cause of Restless Leg Syndrome, in most cases, but some factors associated with its development or worsening include iron deficiency, diabetes, pregnancy and certain medications.
Restless Leg Syndrome usually affects the legs, but can also affect the arms and other parts of the body, explains WebMD. The symptoms include uncomfortable feelings that cause an irresistible urge to move the legs. These feelings are sometimes referred to as "creepy crawly," "itchy" or "pins and needles," and typically get worse when the person is sitting or lying down. Doctors suspect that genes are a factor in Restless Leg Syndrome, because almost half of the people who suffer from it also have a family member with the disorder.
Some symptoms in the arm that are common in Restless Leg Syndrome, such as numbness and tingling, can also be caused by conditions such as nerve injury, a pinched nerve from a herniated disk in the back, nerve problems from enlarged blood vessels or lack of blood supply to the arm from conditions such as atherosclerosis or vasculitis, according to Medline Plus.