Woke up at 4 am with sore tongue and numb underneath, hard to talk clearly. all gone by afternoon.

Numbness is not norm: Numbness is not normal and Numbness does not usually come and go. The two most common causes are infection and impingment. See a neurologist.

Possible trauma?: Waking up with temporary soreness and numbness of the tongue would seem to suggest that something was pressing on the tongue during sleep causing compression of a nerve in the tongue, as well as soreness. What that could have been is up to speculation Having a seizure during sleep could be one possible explanation.