Every time i understand that I’m dreaming,everything goes into grey colours and i wake up,it happens in millisecond when i understand that. What should i do ? 
Well if you LD count from profile description is right and if you only had 3 LD’s then don’t worry, it’s normal, you need to get accustomed on idea of being aware in a dream. I’m fascinated too why the dream collapse so fast for unknown reasons but still time and practice nothing more…
And whenever you realize it’s a dream, try and grab something fast to get the feeling of the dream!
I experience these kind of moments when I become lucid at the very end of a dream. Our conscious part of the brain powers up as we are about to wake up. Sometimes, your mind wakes up while you are still dreaming. This causes the “lucid for a few seconds” efect as the dream ends shortly.
Thank you,next time i’ll try to grab something arround 
Weird, it’s completly different for me 
When I become lucid, I can’t wake up even if Im really over-exicing or trying hard to… I just cant to wake up, but I don’t care since LD is awesome Never woke up from LD at the beginning
So how do you wake up ? 
I always forget that part… I guess REM just ends and I dont remember how it ended.