My mum has frequent numdness on her left hand, during sleep. and wakes up with tight movement of her fingers. what could be the cause?

Carpal Tunnel: This is likely carpal tunnel syndrome, a compression of the median nerve at the wrist. People who perform repetitive or fine tasks with their hands, eg typists, are at most risk. If there is doubt, a nerve conduction study can diagnose for sure. Treatment can be as simple as a brace or as complex as surgical release. Rarely can be associated with hypothyroidism or other issues but most often not.