Strange sensation when attempting WILD

I always experience an interestingly cool but scary sensation when attempting WILD which prevents me from going further. Essentially, as I relax, one of two things will always happen:

1 (most common) - I see an image in my mind. I also feel a light shaking sensation an if I were nodding my head. The image size will warp and distort, yet stay the image will the same. It eventually gets smaller, but yet it seems so large. It is almost impossible to describe in words, the best thing I can think of is four dimensional-esque.

2 -I experience rocking sensations or spinning sensations.

I can never get past this stage of trying to keep my mind awake as my body falls asleep because the sensations freak me out somewhat.

What are the explanations for these? Are they normal and if I let them continue will I eventually enter a lucid dream? And does anyone else experience these?

Do note that I have never had a lucid dream before.