Jocipher,
I am sorry that you are feeling an increase in anxiety today. I know all too well what you are going thru. I too suffer from health anxiety. Always thinking every little sensation is something serious and that I will die. When you are feeling really anxious, try telling yourself "its just anxiety making me feel this way, I have felt this way before and I was okay. I will be fine this time too!"
I tell myself that a lot during the day. You recently had the cardiac monitor as you said, recent blood work, chest x-ray.. those are all very reassuring tests. I just went thru the same things as I was convinced I had something terribly wrong with me. Anxiety keeps our central nervous system on full alert with the "fight or flight" response kicking in and making symptoms more apparent.... that alone can cause fatigue.
I was dealing with the flutters and a weird "hard" thump of heart in chest just a couple of weeks ago. I went to see a naturopath about it because I wasn't getting answers from my PCP that I was reassured with and since I have been working on better managing my anxiety (thru CBT therapy, better diet & positive self talk as well as a natural supplement called GABA -gamma aminobutyric acid) I have had less symptoms. I am still suffering from dizziness, but I am working really hard at not going into a panic everytime I feel it and its getting easier to deal with.
Just know that you are not alone, and you will get thru this. Anxiety is something that is really hard to deal with when its really forefront, but it is managable and you will regain your life :) Have faith in God and faith in yourself.