Preoccupied with death?

recently ive been quite depressing. ive had pretty ****** up life in the past. several things have led me to be depressed and very morbid. at one point in my life i used to cut myself. i have stopped with the self mutilation but still have depressing thoughts. my life has gotten better though i recently moved out away from alot of what had been causing me stress before, and then i was robbed in my own home. gun to my head tied up and everything. my life quickly went back to normal though and im actually doin ok. there is nothing immediate that should be making me think the way i do because everything in my life seems okay. what i mean is im happy and my life is going alright but yet i still have these horribly morbid thoughts at times. for example, for about a week my only goal was to make sure i had a cd of songs made so my family would know wat to play at my funeral. and one night i was thinking about life and how hard life is and how many challenges i still have ahead of me. and i thought "well, if it gets too hard, i can just commit suicide and i wont HAVE to deal with it" and i calmed down. all the anxiety and stress i had at the moment disappeared. i realize that that's not the best way to resolve things. and its terrible to think like that but im wondering why? why am i thinking this way? any ideas? suggestions?