At least you know what he/she thought of you? I don't know if your pills made you act funny for them to be suspicious or not but just explain the situation. If you get fired or anything just go to the higher ups. :)

Hey OP that sucks, at least you know your boss is an ass Hope the recovery goes well!

Your boss sounds a bit judgmental...

Well he kind of was right

Surely your boss knew you were recovering from surgery right? Maybe he was just joking.

Your boss knew you were taking pain pills for a recent surgery. Hopefully he alerted the media as well.

Tell him to buy a trampoline since he likes jumping to conclusions so much

If he didn't know you were recovering from a surgery, which is unlikely, then just explain the situation to him and hopefully he will understand. If not, well you can't fix stupid.

How did he become somebody in charge?

Those pills have been prescribed to you, he can't say shit. All he has to do is call the doctor that the pills were prescribed from if he doesn't believe you. Which he should have known considering you probably had to take some time off from work to have the surgery done. He would had to have granted you time off from the surgery so he can't be jumping to conclusions about you. Don't worry op, brush it off and take care of yourself!