Thank you for the information,
The numbness during sleeping can be due to pinching of a nerve or its root in its course , in the spine or in the limb.
Obstruction to blood flow from any posture is also a possibility.
The other common causes like low calcium or electrolytes, vitamins , thyroid
diseases, diabetes, or any nerve diseases,seems less likely here.
You need to see doctor for an examination
If he feels some tests or imaging studies can be taken.
I hope this information will be helpful.
Please ask if you need any clarification.