Does it matter if it comes from a mental illness? Are you saying that you'd like to explore this Bec it's a side effect from a med?

I don't think the 2 go hand in hand. IMHO.

I think fetishes are just that. A fetish.
I'm heavily involved in bdsm & have a RACK player. We explore safety issues a lot esp if it's something new. I highly recommend you do some homework so you don't cause damage to yourself. Yes FL has a ton of info to glean from so u can enjoy your play.
Much pain play is based on endorphin rushes. This might be what you're looking for. But remember with every rush comes the down side of it too.

Enjoy & be safe. So nice your partner is willing to learn & help too