I'm sorry you're dealing with a mystery health condition, and especially so young. I've been through much the same. Eventually, gradually, you come to get used to how your body works now and health(/death) isn't always at the forefront of your mind. Hobbies and distractions do help, even something as simple a reading, watching movies, listening to audiobooks, bird-watching, whatever works best for you.
I would also recommend that you measure your heart rate and blood pressure while lying down versus while standing up. This is how I found out that I have postural orthostatic tachycardia syndrome (POTS) -- which is a long name that means, essentially, my body cannot properly regulate my heart rate, causing it to skyrocket when I'm not laying down. It's not an uncommon condition, but it is one that most medical professionals will not think of to test for.