From the symptoms you report he seems to have had a minor head injury
. Given the fact that there has been a brief period of unconsciousness
to the incident, has ongoing drowsiness
and headache, it is very important that you take him to an ER or A&E immediately. he doctors who assess him there may decide to perform a CT scan of his brain to make sure that there is nothing more sinister than a concussion
. Sometimes it is worthwhile to have such a reassurance.
They will also look at the gash on his head and see if that needs stitching, gluing or taping.
Hope this helps.