Actually there is a way that helps A LOT. immediately when you wake up, turn on the TV and put it on a channel with a good show or movie and concentrate on it for about 5 minutes. This is from someone who went through the worst nightmares possible . This works if you do it right away.
A good way to avoid remembering your dreams is to stay focused on different things. Try to make yourself busy with something else whenever you feel like your mind is getting centered too much on your past dream. For instance, you can opt to listen to music or share stories with your friends so you keep your mind busy.
no, it is mentally impossible. if your subconsious mind has been scarred from a past dream, ( another way of saying that if your dreams had a great affect on you ). if you had a memory that was horrific, your brian grasps these moments and holds on to them. your brian 'accidentaly' does this because of the state of shock it went through at the moment your dream/experience happend. it is then 'engraved' into your mind, and if it is a bad enough memory/dream, anything that is related, or even distantly relatted can trigger the replay of that moment -theComing Inc.