Hi Jad! I'm so glad this site is helping you out!!
It's hard to stop the cycle. Luckily, I don't have near the anxiety I used to. I don't go from worry to worry like I did a few years ago, though if I get a funny symptom or hear something scary on TV, then the anxiety can creep back up!
The best advice I can give is to fill your mind with other thoughts. Crowd the worry out! Engage in a hobby, or read books that have nothing to do with health. As they say, "An idle mind is the devil's playground," so if you leave your mind "blank" all sorts of scary thoughts are likely to creep in. I've been reading about ancient history, for example. (Normally, all I read is about health-related stuff, pretty much.) Think of a subject that interests you and start checking books out at the library. If nothing in particular interests you, go to the library anyway and look for something - anything. You have to TRAIN your mind not to drift over into that dark place of "what ifs."
I also do visualization. I'd heard about it for quite some time but thought it sounded kinda silly. Well, I decided to try it and - whaddya know - it works!! I visualize a room, like a bedroom. The walls are a peaceful blue, and there is a window with the sun shining outside, looking out into a lush green backyard. Now, arrange your room however you like... Picture where you're going to put certain thoughts. My example: Below my window is a chest, on the floor, wherein I place (bury) thoughts of issues I've already dealt with and no longer need to resurrect. Slam the door on that thought. I then visialize my favorite air freshener scent, and spraying my room with it to clear the air. As I'm doing that, I take in a deep breath, pretending I can smell it. This works great for me, for some reason.
I also have a punching bag in the corner, a fly zapper hanging from the ceiling (ha!) to immediately zap thoughts that creep in (seriously, I imagine the thought hitting the zapper and the thought disintegrating), a door to the left that I can open and sweep thoughts out, a shelf to the left of that where I can place a concern to deal with later, if it's something I can't bury, and to the right I have a cabinet where I place bad work experiences, and I wrap the issue up in a box, place it inside, and shut the door - and lock it. Sounds pretty elaborate, but I must say it's really helped me. When you've really got your room mentally arranged just so, you can totally picture it, it works. Also, remember to look out the window after you've either buried/locked up/disintegrated your thought(s) and gaze upon the lush garden and enjoy the sun out the window. Take a deep breath and smell that favorite scent.
It'll take some practice, but again it's about training your mind to obey you, rather than you being a slave to your mind.