This is most likely from compression of one or more nerves in the wrists and hands. The most common nerve compression is carpal tunnel syndrome, where the median nerve gets compressed within the carpal tunnel at the base of the wrist.
The median nerve supplies sensation to the fingers on the thumb side of the hand.
You can also get compression of the ulnar nerve. This nerve can be compressed at the wrist in Guyon's canal, or at the elbow, in the cubital tunnel.
The ulnar nerve supplies sensation to the fingers on the small finger side of the hand.
It is not uncommon to compress these nerves by the way we sleep. When we sleep, we tend to bend our elbows up and put our hands under our chin. These positions can compress these nerves.
It tends to get worse as we age and is more common in females. So, the middle age female is the most commonly affected patient.
If the numbness is waking you up, or it lasts for longer than a couple of minutes, you may need to have your hand evaluated by a hand surgeon.