I'm not sure if I'm the only person with these problems but try not getting visual blackness while you do things like:

-turning around really fast
-walking through walls
-accidentally closing your dream eyes
-focusing on your thoughts or feelings and losing the surroundings
-focusing on an object losing the surroundings
-walking into a new place too fast and suddenly not being able to dream what it's like. Flying too high can also do this.

You can do what ever you like but try to focus on these while you do it. I have a really hard time with these.