Stop thinking about dying I used to be same I always worried about it as you get older you stop worrying so much . Do things you love keep your mind active and always think your the best . Life is for living so live worrying will only get you down . And believe me there's never any end of life honest I've seen stuff that I can't explain .I know what your going through I hope I've helped you ;-)
Instead of obsessing about yourself and your mortality, think about doing volunteer work. It will help you to get out of your own head, appreciate what you have, and learn the pleasures of helping others (and there really are pleasures to be had this way). To find something which appeals to you, go to www.volunteermatch.org .