While i may not have had the same thoughts or dreams as you, i think i have felt something similar. For a very long time i have had nightmares, where i have been bullied, left alone, or have everyone i love die. I have considered suicide and many other bad things that i would rather not talk about. Most of it i think comes from my own life experiences. I have been bullied, chased, beaten and left alone on so many accounts i lost track. However i remeber each one so vividly it's like it happened yesterday and sometimes my mind will wander back i feel these horrible events again and again. Which brings me to my point. I'm no therapist, but my best guess is that maybe there is something that has happened in your life that has made you think this way. Or possibly you are feeling this way because of your lifestyle. Unfortunalty i don't know you personally or anything about you, so i can only take guesses based on what you have said so far. My suggestion however is to think back and figure out whatever has made you feel this way, that is normally the first step to solving something like this.