I can understand your concerns. From the history you have given regarding a history of fall and trauma to head with unusual change in behavior and drowsiness
and headache, one should always consider ruling out head injury
. The best way to do it is by getting an MRI/CT head done at the earliest. If you wish to stay back and observe, vomiting
and visual disturbances and altered state of consciousness and confusion are something you should look for. if any of these symptoms develop, you should not wait longer.
I guess I am able to solve your concerns.
Hope he gets well soon.