I’m 24 and about to be 25 I’m constantly feeling like having a panic attack even fast heart beats. I know death can come at any moment and it’s just that fact alone that someone can just kill you. It’s the fact I don’t go anywhere that kept me alive. I hope to be alive from an older age but I haven’t done anything useful which I’m sad about death. I’m sad I smoke as well I’m sad that this means I’ve mostly killed myself. You know what actually does happen? If death is just like sleep that might be peaceful but there’s not really another chance at living. If it’s something then it’s like I might see people I don’t like I miss people in some way but not being able to see them again because they committed suicide or some other stuff. I don’t get it anymore actually and just kind of wait which I hate.
Smoking doesn’t mean you’ve mostly killed yourself. You can quit and regain your health.
If you like to read, I recommend The Five Invitations by Frank Ostaseski. It’s a look at facing your own death from a Buddhist perspective. Also When Breath Becomes Air by Paul Kalanathi, a man who knew he was dying when he wrote the book. I have found that learning how to face your mortality instead of ignoring it is much more comforting.
As for an afterlife, there is zero reason to worry about that because we have zero information about what it would be, if there even is one. I live my life the best I can and trust that if there is something after, I can react to it then.