I have HUGE health anxiety! I can totally relate. The smallest ache and pain becomes a terminal illness :)
I don't have it 100% under control by any means, but here are the steps that I took a few months ago that really helped:
1. I had a physical. Totally healthy.
2. I stopped researching on the web. It doesn't help - it only makes you more nervous.
3. I used a CBT log sheet that my therapist gave me (I started making copies and writing down...now I can "complete" the form in my head). Basically, when you feel a pain, shortness of breath, etc. - on the left hand side you write down what your mind immediately goes to (I'm having a heart attack, I can't breathe, I'm dying, etc.). Once you have completed that list, you must write a percentage down of how much you truly believe in that statement (from 0-100%). On the right side of the paper, you write down more positive/logical thoughts (I overate and have indigestion, I ran up the stairs and I'm lightheaded, I slept wrong and my shoulder aches, etc.) and then rate those thoughts with how much you truly believe them (0-100%). I'm sorry if this sounds complicated to write - I wish I could just show you - but it really puts things in perspective!
Good luck! It's the WORST. I'm a total hypo too, so you're not alone :)
Panic Attacks (since age 10) & General Anxiety with a little OCD thrown in there
Biggest Challenge - Panic; Biggest Joy - my 3 cute kiddos (ages 1, 2 & 5)