I tried LDreaming for the first time last night and it was a horrifying experience. Everything was shaken, sounds were so loud I couldn’t hear myself screaming, I saw myself floating on my bed.
What’s this all about? Has anyone encountered these sorts of problems when starting out…i’m telling you it was worse then a bad LSD trip.
Slight Edit 
But again, you dont just go lucid dream. its not like ice skating. you dont just mosey over to the rink and skate. you probably just had a normal dream, and - being more concious and thinking about dreams, had a vivid ND. this is what causes the expiriences.
you probably had plenty of scary dreams, but only now noticed it because you started thinking about dreams.
Once you can look at all dreams positively, the word ‘nightmare’ becomes nothing. then you will look forward to all ND’s no matter what they are about.
Did you had SP? I mean, did you found that you were unable to move your body and you were like paralyzed?
If so, you had an OBE that is closely related to LD (so closely, that you can call it LD actually). It’s nothing to be afraid off. If you get used to, SP can be great target to induce LD-s.
BTW, i bet you only “screamed” in your head. It means, that all you experienced was a start of a dream, and it all happens in your head, not in real life. So nothing to be worry about 
So far it is an isolated incident. It sounds like it could have been SP. But even if it wasn’t, you can’t expect every lucid dream to be like that. Try again and see what happens!
shrug nightmares happen. Lucid dreams are all about awareness, and so it may just be you are simply more aware. I’m not going to repeat whats already been said, but I do have another theory.
I’ve heard that when trying the WILD, people will get much stronger hypnogogia. They may also have “audio hallucinations” so the loud noices and the things you saw may have been just that. Unfortunately I’ve never experienced it myself, so I’m probably not the best one to fully explain and it may have happened even if you weren’t intentionally trying WILD.
The part where you saw yourself floating above your bed…I’ve expericned something like it in dreams, where I switch perspective; I’m watching myself from a third person point of view. It has also happend deep in meditation when I felt myself just float out and I saw myself-I guess this is what they call an OBE. I’m not sure if the OBE will apply to dreams though…I’m kind of curious now actually.