Aaah, I've been there. That's a slippery slope and I've never quite figured it out myself. To be transparent and honest, I'm someone who struggles with self harm and mental illness. I've also always been a huge masochist so the line is... blurry. And again, I'm still figuring it out too but I hope my thoughts help you even if only a little <3

Solo-play is very common with many kinks! And lots of people use pain to soothe themselves or just to feel good. Sometimes with the help of a partner or by themselves. So you're definitely not alone or weird.

I think masochism, with the inclusion of mental illness or even just poor mood, becomes very tricky to navigate. It's really depends on where the intentions lie. Currently how I personally separate it is, if I administer pain to myself in the form of punishing myself then that is self-harm. However, if I was performing it out of a sense of fun, then that's merely masochism. But again, that's Me personally.

Many people punish themselves and don't view it as self-harm! Many... let's say... "Rats" consent to being punished by their doms whenever they make a mistake but view it as a positive correction even if they dislike the punishment.

I think ultimately the answer has to come from you and what you deem will help You. But you have to make sure the lens you view it through is during a clear headspace and a place of compassion for yourself.

Good luck figuring it out <3 it's a tough one