About DEILD and dry spells

I've been training on DEILD lately,
not moving and visualizing your dream you want to enter.
I don't understand why some people have such huge dry spells if DEILD works like 95% of the time :? .

Another thing I want to mention is I visualized a DEILD.
It was me falling down from space, but I fell down too hard that it felt really bad, and I'm not talking about falling like this :http://www.youtube.com/watch?v=z-9r-DI7HmM speed but really 50x that fast, how can I control my visual induced DEILDs? Just practise?