Based on the symptoms described—head injury, brief loss of consciousness, and current sleepiness and disorientation—the most likely option is that this person has a concussion.
While intoxication and seizures could cause similar symptoms, the context of a recent head injury points more specifically to a concussion. Meningitis typically presents with other symptoms such as fever, stiff neck, and sometimes a rash.
It's important that this person receives medical evaluation as soon as possible.