Judy's answer is great. Other expressions include: Did you hit your head? Did somebody hit you in the head? Did you forget to take your medication (meds) today?

Were you dropped on your head as a baby is something that would be asked in the UK. HOWEVER, you would only say it to someone you know well as a joke because it's a pretty rude thing to say

What was that? A brain fart? Put your brain in gear before running your mouth.

I think, "Did you get hit on the head or something?" would be more natural... I don't think this is something we say much though!

A little more common is, "Did someone drop you on your head when you were little?"