Hello, and nice to meet you.
I sometimes dissociate during sex more than I would even like to think of. While it has gotten much better for me, there are times that the smallest thing can trigger me and poof, I'm gone. Sometimes it can be for a brief moment, sometimes I go completely and sometimes it just diniminishes what I experience. It is hard to tell what will happen with me at times but I was abused on almost a daily basis from the time I was very very little until I left for college. My body is still confused at times what is going on and if it is ok or not.
Fortunately my partner and I are both survivors so that probably helps us in some ways. But from the day we met, we have had a standing rule of understanding between us. If at any time, either of us needs to stop, all we have to do is say "stop" and we stop. We don't have to give an explanation at the time if we can't articulate it and we don't have to worry about anything else should we need to stop. Later we do try to talk about what happened so that we keep the communication open between us, but we have both been very respectful of each other. Without that, there is no way that I could even be intimate with my partner or trust him. It has helped so much and we've been together over 4 years now.
Take things slow with the person you are getting into a relationship with. I am not sure that you need to tell them your entire life history, but maybe an indication that you have had some past trauma in your life may or may not be helpful. You have to be the judge of that in the situation you are in. Just make sure you have your boundaries in place and you take care of yourself. Trust your instincts and recognize the fears for what they are.
While I may be simplifying a lot of stuff, I do realize it isn't as easy as it seems. It has taken me time to trust someone but with each day that passes, I trust and love my partner so much more.