Zoning out is fine if that is your intention. Tell yourself that at the end you'll wake up refreshed and you do then you've been getting it.
Paraliminals are a good way to get completely relaxed for 20 to 30 minutes and not being aware of what is being said is perfectly fine.
We don't recommend that you use any old paraliminal just for falling asleep though. They work best by you stating a clear intention about what you are working on or listening to that particular paraliminal for.
Alex
