dude i haven't had a nightmare since I was like 7 years old, its all in your mind. First of all, If your scared of nightmares, then your going to have nightmares because your thinking like that. second of all, the best way is to become lucid so you can confront whatever is scaring you in your dreams. But I guess your scared of lucid dreaming too or something? The only way to decrease vividness is to be lucid so your gonna have to become lucid either way :p