Why does this happen?

Hi all. Last night, I was going to try WILDing by waking up naturally, which I haven't really done before (natural WBTB). I've always used an alarm.

Anyways, a day ago I repeated, "I will wake up naturally." Which didn't seem to work. So instead last night I said a couple of times in my head when I was falling asleep, "I (will) wake up naturally after 5 hours." That seemed to work! The time was pretty close since I didn't look at a clock when I said it. Anyways, when I woke up a little after 5 hours, I heard two large booming sounds, like someone was trying to break in. Then I was aware that I was awake. I stayed still upon awakening. I didn't dare try to stay still any longer because what if it was an actual person trying to break in? Sure enough it wasn't though.

I woke up one more time naturally after that, all the while staying still. I didn't get lucid, but I remember right as I woke up something stuck into my mind from the previous dream, like I was just there and now I'm in my bed.

It's weird. Why does this happen?

P.S. Also when I wake up, I stay still, but I don't feel like I'm in SP.

Although there are those who may disagree with me, in my reading and studies SP accompanied by loud noises is the beginning of an astral projection experience. In my opinion you were about to leave your body.

You can test SP, and break it, simply by thinking about moving your pinky. You can return to your body, if you leave, the same way. In the in-between state try mentally thinking out loud, "Now I leave my body!" or "Now I Lucid Dream!" - whichever you wish to do. Use your own words, state your intention as loudly as you can in your mind as if it were a command you expect to be obeyed.
- DreamBliss