BDSM Help

I just recently (as in two days ago) had my first BDSM experience. I've been sexually assaulted in the past, and was in an abusive relationship so the guy was prettty "vanilla" to make sure I was okay. Now, I cannot stop thinking about it; walking around at work imagining him slamming me against the wall, spanking me, biting me, etc. I've never done anything like this before and I'm just looking for advise on how to proceed to the harder stuff without triggering something from my past... any suggestions?