Now I don't want to freak you out by saying this but my grandmother died by falling down the stairs because she had an unusually weak point in her skull.

I don't know how common this is since you'd have to be hit on a weak point to know it is there.

Just might pay to work on your defence a little more to prepare you for your next hard sparring session.

I've never been hit right on the top of my head with a punch coming from above despite being short and I'm not exactly Ali.

It probably won't take long to correct your technique enough to prevent this happening again.