Is it normal to constantly think I'm dying

its ok, everyone has to realize their mortality at some point. for you its happening now. when we are young we live like we are immortals. thats the illusion of youth. but that changes. you are gonna watch your body decay, sking hanging, getting tired, gray hair and/or baldness, lower to ceasing sexual desires. and it happens over so many years... and when that process has run its course for enough time, this dreaded biological shutdown called death happens, to all of us. so my advice to you, live for the moment. cheers