I realize i'm dreaming and then my dream turns into a nightmare.

[PeterSheen]

I'm new to dv and have never had a lucid dream. I have done a lot of research on lucid dreaming and been interested by it for a year or two. I have pretty good dream recall but nightmares can sometimes be a blur. Anyway, A couple days ago I was dreaming and I realized it. I remember I told myself in the dream "I'm dreaming" and I kept trying to attain lucidity but instead of turning lucid my dream turned into a nightmare of sorts. I felt cold and very scared, my vision went black and my body started to tingle(like when your scared). Then I got so scared I woke up. Their wasn't anything scary about the "nightmare" but I felt scared genuinely scared. It has happened multiple times and one time I tried to avoid waking up and face the nightmare and i started seeing a skull spinning slowly in front of me and my body just kept tingling more intensely before waking up. I have never had a nightmare like this(that im aware of) randomly it only happens when i tell myself I'm dreaming and i try to achieve lucidity. It's like my sub conscious doesn't want me to lucid dream. Anyway I've tried researching this and haven't found anything so I'm wondering what this means. I've come to the conclusion that maybe I'm dreaming everything and my brain isn't actually becoming active and starting a lucid dream I'm just dreaming that it is(If that makes any sense). Has anyone else experienced something like this? P.S.- I don't think I'm becoming overly excited and the nightmare is triggered from my eagerness and excitement of realizing i'm dreaming because I stay relatively calm and relax myself as im trying to attain lucidity.