Abrupt endings to somewhat stabilized dreams

Recently i have been able to finally stabilize a couple dreams which was quite a task for me as it's easy to get lucid but hard to keep. so in 2 or 3 of these somewhat stabilized dreams (im not sure if they were fully stabilized) i have had as the title says abrupt awakening such as:

1) im in my room i try and stabilize it works so i proceed to jump out my window before i can i hear a *THUD* and im awake (I did RC's)

2). im in a store stabilize once more and i look around seeing what kind of things they have. i turn my direction to the ground i see a little stool it almost teleports two inces closer i think oh-crap (still don't know why) and BAM awake!

So why does this happen is my REM time over or am i doing something wrong?

I have this exact problem as well. The dream will be going strong and all of a sudden I'd realize I'm dreaming. Then I instantly wake up. For me I think I figured it out, I think saying out loud that I'm dreaming wakes me up. I don't know why but every time I say it I instantly wake up. The thing is though I can't help to say it and it always happens.

As for you though, from those two examples it looks you did or saw something shocking. Maybe this is waking you up in shock, kind of as a defensive mechanism? Have you tried calming yourself down completely while also stabilizing the dream?