Stemetil as it's called here is pretty heavy duty stuff to say it mildly.

The Benedryl was probably to help counteract the effects of the Companzine.

You must have been in a really bad way to have those IV. Do you have very bad migraines all the time or just post injury?

I think it's pretty common to have reactions to that drug. I don't think the reaction would necessarily be related to having a head injury, but I'm not a Doctor. Years ago when I was nursing we used to give it to patients all the time post-op though.

I was actually prescribed it post head injury myself for a short while. It made me edgy and didn't help the vertigo anyway.

My daughter however had a really terrifying reaction to it in the ER setting once. She had some major problems with one kidney that had gone undiagnosed all her life. She was in a very bad way to begin with but they gave her Pethidine for her pain and then Stemetil to stop the nausea and vomiting. To this day she still remembers that terrifying feeling after getting the Stemetil injection.

I hope you're feeling better.

EDITED later to add:

I found some places where it says "contraindicated - head injury", but when I looked further into it all it appears to mean very serious head injuries including subcortical brain damage and coma from what I could tell. If you're concerned please talk to your doctor about it.

I also forgot to ask, did you go back to work?