Lucid Nightmares

I've been having a lot of nightmares lately, except they only happen after I become lucid. I will get excited about being able to control my dream, then the dream fades into a false awakening. I'll often hear screaming or see blankets moving and breathing heavily. Since I've been having a lot of lucid dreams lately, this happens often. Any way to prevent this? (by the way, I had a 30 minute long lucid dream yesterday without nightmares which was awesome)

This has happened to me before. Actually I went through a long period of dark and creepy lucid dreams often followed by non-lucid nightmares. After a period of time they became less and less common. I don't know what caused them to start or why they went away, its a mystery to me.