Hello XXXX, Thank you for posting your question on HCM. If I was your child doctor, I would recommend for you to observe him in the next 24 hours and be very careful if: -- you notice any new behavior in your son, -- if he falls asleep not in his usual time, -- try to do something with him in the next hours after the head hit, even if its sleeping time, to keep him as much as possible on observation for strange/new behaviors that you can not see while he is asleep -- and check him from time to time while he is asleep. Things you should look in his behavior, that should make you take him to the Er department are complaints of headache, dizziness, nausea and vomiting, difficulty with coordination or balance (not being able to catch a ball), feeling, confused and dazed, difficulty concentrating, thinking, or making decisions, trouble remembering things, such as what happened right before or after the injury, slurred speech or saying things that don t make sense, feeling anxious or irritable for no apparent reason, feeling sad or more emotional than usual. Hope this helps, Regards, Dr. Klarida