I totally understand what you are going through. I have suffered from anxiety for the past 12 years and it gets better then I have times that aren't so good. Right now is one of those times that I am struggling.
Anxiety is a great trickster in that it always returns with symptoms that are fairly new so that it keeps me thinking something is really wrong this time because I've never felt like this before it can't just be anxiety. 3-4 years ago I wore a halter monitor as I was assured something was wrong with my heart, when it only showed tachycardia, no heart problems. For whatever reason now, I'm having weird sensations in my head and chest that are making me nervous that something is seriously wrong this time.
I've been keeping a super close constant eye on my heart rate which I know makes it rise but of course I can't get myself to really believe that's all it is. Some reassurance that everything will be okay would be much appreciated right now. Thank you <3