One thing that personally helped me recover mentally was weightlifting. Part of what helped was that I could relatively easily attribute any random (and benign) ache/pain that I might otherwise worry about to "oh, well, I just lifted recently, so my body's repairing/sore/etc" as opposed to some serious condition I found on Google. Sticking with caffeine even though I was worried about palpitations also helped me through some form of "exposure therapy," where I eventually (re)learned that caffeine is safe to consume.
Talking with my therapist helped. As did consciously reminding myself that, for a lot of rare or potentially deadly conditions, the symptoms would be much more severe than I'm experiencing, and that some symptoms (fast heartrate is a big one) can be attributed to anxiety alone.
For example, last night while lying in bed, I felt a sudden twitching on the left side of my chest at about twice my resting heart rate. I instantly jumped to the conclusion that it was my heart having rapid contractions, which triggered a burst of anxiety, but when I stopped and thought about it (the twitching seemed to be intermittent and didn't feel internal like a heart problem might, it felt external), I successfully convinced myself that it was my muscle twitching -- a totally benign occurrence. Maybe I was dehydrated.
Basically, I was able to help myself by using logic and trying to match the severity of my personal diagnosis with the severity of the symptom I was experiencing. I imagine this wouldn't be possible if I suddenly had symptoms as severe as GP, but it can help me stem these threads of anxiety before the anxiety itself causes more issues than the original problem.
However, it is a well-known fact that caffeine and anxiety don't blend very well. Be careful.