Sometimes, I wake up in the middle of the night and my arm is cold and stiff. My hand is blue and it looks like I’ve lost the blood supply to my hand. What causes this?

The condition you’re describing is called positional cyanosis. Cyanosis means a “bluish discoloration.” It’s caused by a lack of oxygen to the tissues. This can occur if you sleep in one position too long or if you lay on the arm without moving for more than two hours.

Another possible cause of this problem is a condition called thoracic outlet syndrome (TOS). In the adult body, there’s a bundle of nerves and blood vessels that travel from the neck down the arm. These pass under the collarbone. If anything presses on the vessels, the blood supply can get cut off.

TOS can occur as a result of postural changes, bone spurs in the neck or shoulder, or problems with the muscles. A physical therapist can help you find the cause of the problem and solve it. If you don’t get relief from your symptoms in three months, see your doctor.