When people say that teenagers feel like they're invincible, this is what they're talking about. The reality of life is that all this stuff starts much sooner than you'd expect. Growing up, you think you're probably fine until you get old but it's all part of a gradual decline that you have no choice but to get used to.
Good luck, buddy!
It may sound stupid but my mental health drastically improved once I started using a password manager.