I've found that by repeating how I WANT to feel to myself, it really helps (this is long term of course...unfortunately, years LOL). Example, if I am SUPER nervous about a job interview - I just repeat to myself I've done a ton, I almost always get offered a job, I know what I'm doing, I am a good fit etc etc I kind of sell myself...to myself. That goes for almost anything...seriously, took me about 1-2 years but now it's so annoyingly natural that my positive friends sometimes snap at me for being so optimistic (I used to be the girl that no one told things to because I was SUCH a pessimist).
I just have this tendency to obsess. Omg Mia stepped weird her knees are going out and he'll be crippled her whole life and I won't get to do agility and have a fun hobby and omg.
Or my car is making a funny noise ergo I'm going to have to spend thousands and push house plans back.
Or or or....
I always find something to worry about.