system
Given the following post, respond as if you're commenting on Reddit:
human
How come I can't make a fist or squeeze my hands tight after waking up in the morning?

I don't mean the hand being numb from sleeping on it.

Is it simply that the body is so relaxed in sleep, it takes a while to regain control of the muscle? Because it seems like only my hands are affected.

Is there a name for the phenomenon?
gpt
From Wikipedia on REM sleep:

"The release of certain neurotransmitters, the monoamines (norepinephrine, serotonin and histamine), is completely shut down during REM. This causes REM atonia, a state in which the motor neurons are not stimulated and thus the body's muscles do not move."

If you wake up early from a sleep cycle, these neuroinhibitors are still in you system making you feel lethargic and makes muscle movement very difficult.