Sounds like the beginnings of a panic disorder or PTSD to me, but the thing is there is usually some sort of trigger, and figuring out what those are is key in managing them.
If your thoughts got you carried away, and then you were getting all that stuff you have to learn to top yourself, and determine if you are just torturing yourself, and if there really is a reason to feel that way.
For me NC was broken too many times, and it left me scarred. I would trigger when he would be texting, and zoned out, I would trigger, when his phone would ring, vibrate, or anything for a while. It took me forcing myself to look at the entire situation, to start dealing with it. Was he being the ass he was before, was he being loving to me now. Was he on the phone for work? all of those things.
It takes a long time to learn to deal with this stuff, but if you are having anxiety issues I strongly recommend you talk to your Dr sooner than later, there is nothing worse than having your first full blown panic attack while driving, or out in public.