I have had this plenty. My hypochondria tends to give me bouts of different things to worry about, and for one certain amount of time I was given this. It feels awful and it makes you feel afraid to breathe. The good news is from what I understand, it is very most likely totally harmless. This is a thing that happens to lots of people and they don't even notice it. We however notice it, and then we get scared, and because we're scared it's more likely to happen again since it can happen more when you're stressed. It's a vicious cycle.
I know I can't tell you it's absolutely nothing to worry about and alleviate everything, but I can tell you that I had this going on weeks and weeks ago and it got better :>