When I was 17, I started smoking a lot of weed, I was a a real shithead, it gave me panic attacks, but at least I felt cool.
Then when I was 19, 20, my new exposed underlying anxiety disorder really took a dark turn, I couldn't go in public without it feeling like I was dying, and of course hypochondriac, and paranoid, I used to think I had cancer, or if I ever had sex, an STD, I used to think I had a huge range of personality disorders, brain damage... anything really,,at one point I thought my roommate was trying to gas my room because I was having difficulty breathing due to anxiety. I dunno why I was so delusional before.
I still am, but my psychology changed, I've matured, I've come to not immediately accept my thoughts as being true, and remembering all times I was wrong
I'm 25 now. Not 100 percent free from hypochondriac thoughts, but miles better.
Therapy helped, YouTube helped, Leo helped.