Cried During Sex For No Apparent Reason?!

All of yesterday, I was feeling very emotionally and romantically disconnected from my boyfriend. I didn’t feel cuddly, I didn’t even want to kiss, I felt like I didn’t even want to be around him, but I wasn’t upset with him and didn’t have any particular urge to be alone otherwise, so I couldn’t figure out why I was feeling that way. We had a couple of misunderstandings later on in the day, but we talked about everything and were feeling much better. We eventually decided to have sex, and I wasn’t consciously feeling upset, scared or in pain in any way, other than a bit of pressure on my uterus, but that’s typical so my brain has learned to ignore it. A couple of minutes in, all I felt emotionally that I knew of was the urge to wrap his arms around me for comfort (we were in a position where this was possible) and I suddenly started to freak out and was like “Babe, I can’t.” and was sobbing before I got any typical signals that it was coming. So he stopped and asked what was wrong, was I in pain, stressed, scared? I told him no, I have no idea what’s wrong and just rested my head on his chest and cried, hyperventilating. Fortunately, he was very good about it, just wanted to comfort me and make sure I was okay. We’ve had sex before and it does get a little stressful sometimes because I have some past issues, but usually I would just bury my face in his neck or hug him for a minute, it’s never been to the point where I felt the need to stop or cried. Any input on what may have caused this? Has it happened to you?