I understand that repeating mantras before sleep helps with LDs. Why? Personally it never helped me, I suspect because I end up on something else at the moment I sleep. I find that reality checks and coming to awareness through the day is the best help for me.

Anyway, to the point - even if you DO manage to keep at the mantra as you doze off, you end up with 4.5-6 hours of non REM sleep. Surely by the time you get to REM your mind would have been somewhere doing something other than remembering the mantra you were repeating 6 hours ago?