Can someone please explain this?

Last night, I was very sleepy and went to bed.
In bed, I found out that I was having trouble getting to sleep, despite being so very, very sleepy. I felt myself getting sucked into my dream, but each time I managed to get myself out of it by a reflex. The first time this happened I opened my eyes by reflex and saw some kind of lit up room with a window with white light coming out of it, after a split second I saw my own dark room again. After this happened, I got the same feeling each time after a couple of seconds when I closed my eyes, so I turned on the light and got myself something to read. It was hard reading because I couldn't concentrate that well. After like 5 minutes I went to bed again and everything was fine.

My question is, what happened?
It was like I was between the transition of being awake and dreaming. Even though I was 100% sure I wasn't asleep for even a second before reading my book. That room is obviously a hallucination, so was it some sort of WILD? I remember my body feeling stiff at some times, which I recognised as sleep paralysis, even though I never experienced that before.

I do a WILD attempt every night on bedtime and I always experience something that i like to call dream flashes. I am not sure if that is what you experienced but perhaps you can relate to it.
As I relax I experience a brief moment of strange sensations like "seeing", "hearing", "feeling", "thinking". For example I can see a forrest and think "The squirrels don't like when Adam say that".
I experience this just a brief second and is then brought back to my physical body awareness and think "Who is Adams and lol squirrels.".
I think this would be called hypnagogic imagery that is the transitional state between wakefullness and sleep.

Does this seem to match your experience?

Yes I recall having them, I remember when I was trying to focus my thoughts on something else and ended up in actually seeing the whole scenario before my eyes.
It's like a 10 second long dream.

It was either really vivid HI or a short NREM dream fragments. Not sure how long it's been since you slept, but if it was around 24 hours, you could have a couple of micro naps, but I'm leaning towards the Hypnagogic Imagery.

Great, did some research on this.
Turns out that the feeling of being sucked into a dream is called a "Hypnic Jerk".
Hypnic jerk - Wikipedia, the free encyclopedia
I have had a lot of these in my past, often accompanied by a noise, like there's a lot of wind blowing by my ears.
I was definitely in NREM sleep/Hypnagogia.