You can't forget, but you can make peace with your past. Everything that has happened has helped shape you into the person you are today. Bad experiences uniquely grow us. Those experiences can teach us compassion, empathy, understanding, patience, forgiveness, so many things! Bad experiences done to us can teach us what we never want to do to another person. Bad experiences caused by us can teach us the consequences of our actions, giving us valuable wisdom to not repeat the action, and also to share that wisdom and hopefully spare another person from doing it. Sometimes just changing the way we look at our past is all that's needed.
Well try to get your mind off it. Usually talk to someone about it or replace your fear with something funny or so randomly stupid that u have your mind on that instead of what you've feared. Ex: MY LLAMA ATE A FLAMINGO WELL HE WAS RIDING A TACO INTO UNICORNLANDIA WHERE HE AND A BULLDOG WITH A PINK AFRO FOUGHT TO THE DEATH IN A BOUNCY HOUSE. I hope in some weird way that helped :)
If it's haunting you not likely you will forget about it. Better yet, talk about it. Straighten it out, except it and move on, or at least, over it. You need to come to resolution, don't carry the weight.
You can't forget your past, no body can forget their past...but what you can do is accept it, and move forward from it. Be strong and let it all go, let your nightmares be free! Let it out, find your inner peace. Talk to someone about it, to help you move on from it. Don't try to push it away. You need to think it over no matter how scary it is, you need to go through this disaster that scared you. Because at some point you have no choice but to face your fears, so you either accept the challenge or run your sorrows forever, and trust me...your shadow catches up with you eventually. Don't let this beat the best of you, have faith! Hope I helped a notch or two:).
Eventually, you're going to have to get this out of you and talk to someone about it. I myself have a VERY difficult time trusting because of these same things-we ALL have had one thing or another that has affected us from our past and then invades our dreams turning them into nightmares . I am hoping this for you ...until you find the right person, a good friend, lover, husband ( or whoever it may be) who you can tell it all to and trust they will help you express your fears (and there ARE good people out there that will help you ) I am hoping for you to take it day by day, minute by minute, second by second, and move FORWARD with your life. Nothing can catch you or old you back as long as you're moving forward, not backwards. I wish for you Peace in your heart.