Why do your hands fall sleep when you sleep?

It's not the case that hands "fall asleep" while sleeping. However, your hands may experience a tingling, numb, or painless sensation. This is caused by a temporary interruption of blood flow to the nerves in your hands.

This can happen when you put pressure on your hands or wrists, such as when you lean on your elbow or sleep with your arm under your head. When you move or change the position of your hand, the pressure is relieved, the blood flow returns, and your hand will usually return to normal.