Wondering About Symptoms For Concussion. On Saturday My 24 Year

Wondering about symptoms for concussion. On Saturday my 24 year old son got hit in the head very hard by a friend's knee when he was doing a back flip. He bit his tongue and it bled profusely. He said he was "out of it for a bit and just sat for a while." He was on the beach with friends and they had been drinking. He seems to be ok but he has been pretty tired. Not sure if that is a product of a long labor day weekend or a symptom of concussion? What should we be looking for 2 days later?