Asthma
The scary thing about asthma, and a few other diseases, is that you could just close your eyes to go sleep and never wake up again. Straight up suffocate in your sleep.
Asthma also happens to be a chronic disease that's never going to truly go away. Even if you beat it now, it will just come back a bit later when you're weaker.
Maybe not in your 30s or 40s. Maybe it'll even wait for your 50s or 60s, all you need to know, is that it'll always be there lurking.