I was literally just thinking about this the other day, about how ancient people didn't notice that people that got head injuries would change their behave or die instantly.

I don't have a single friend whose behavior I'd have noticed changing after a head injury: the only reason I know it happens is because I've read case reports of it happening to someone. Maybe some doctor might have noticed, but then, I'd expect ancient peoples to also have fewer head injuries that were serious enough to change behavior but also mild enough to be survivable.