I'm not sure if there was a significant time that it happened to me. I just couldn't stop... couldn't go through a day without si'ng .. usually more than once a day. And it took hospitalizations and years of therapy and dbt therapy to break it from being habitual. However, every now and again I might si, but with the tools I have learned along this path at this point I CAN stop myself.
If you can find a way to stop this now..... please do..
If you have a T, talk about distraction techniques... ask people on here how they work on turning the urge into some other action...
I hope this helped a bit...