To dream that you commit suicide represents your desperate desire to escape from your waking life. You may be harboring feelings of guilt that you cannot get over and thus turning the aggression on yourself. You need to start approaching problems from a different angle. Alternatively, the dream suggests that you are saying good-bye to one aspect of yourself and hello to a whole new you. It is symbolic of a personal transformation or a new stage in your life.
To dream that you kill someone indicates that you are on the verge of losing your temper and self-control. Consider the person you have killed and ask yourself if you feel any rage towards him or her in your waking life. Your dream may be expressing some hidden anger. Alternatively, you may be trying to kill an aspect of yourself that is represented by the person killed. Identify the characteristics of this person and ask yourself which of these qualities you are trying to put an end to.
To dream that you have been stabbed signifies your struggle with power. You are experiencing feelings of inadequacy and defensiveness. Alternatively, the dream suggests that you are feeling betrayed as reflected by the popular phrase, "being stabbed in the back".
I got all of these off the Dream Dictionary, which is usually pretty accurate when I use it for myself. Basically it seems like you just need to find a way to just de-stress before going to bed, because stress affects the way you fall asleep and what your mind thinks for you. Usually I drink a cup of tea (decaf) before going to bed and it usually helps me relax and have better dreams.