There are people that wake up with swollen body parts and there are various reason s for it.

Reasons for the swelling:

Dehydration

Dehydration is caused by lack of water in the body. When this happens the body starts saving the remaining water in the body which causes swelling of the limbs.

Sleeping posture and duration of sleep

Sleeping on your stomach and on your side is not recommended since it may cause joint ache. Insomnia or insufficient sleep may cause swelling.

High level of sodium

If you have excess salt in your body it will detain water.

Kidney diseases

This organ is responsible for detoxifying the organism and it is not working properly it will detain water.