I don't know if sleep "learning" is the best name for it.
Studies being done in the German University [Lubbeck? have to find the article to be sure]. Has shown that the brain continues to try and find a solution to perplexting problems we encounter during the day.
We can give the mind a problem to solve during out sleep, by presenting it to our mind just before sleep but how many of us manage to stay focused long enough just before falling asleep?
Paraliminals don't solve the problems for you they trigger your own mind to discover the solutions. So starting with a Paraliminal just before sleep helps to focus your mind on the thing you want a solution to.
Based on my research into the subject. I wouldn't use the same Paraliminal night after night nor would I cycle the sleep learning part endlessly thoughout the night. All things in moderation 
Alex
