Anxiety sufferer here too. Health anxiety was one of the main areas as well. I use mindfulness and meditation as one of my tools, I also have greatly reduced my caffeine and sugar intake. Trying to get exercise helps as well. I also see a counselor from time to time and that helps keep me focused on my tools as well as helping me find new ones.
Specific to the health anxiety thing, i'd say get rid of the fit-bit or at least turn off the real-time heart rate monitoring. That in itself can create anxiety.