Hi Stevie,
The difference for me is that when one is tired they will generally fall asleep and regardless if they're mediating or not. But for me when I go unconscious (more noticeable when meditating sitting up) I can feel the binaural beats pushing against my nervous system and I can feel myself being drawn down deeper, to the point that my head begins to flop around and I either come back out of it or find myself several moments/minutes later aware that I must of gone unconscious. Quite strange at the time and the wonderful feelings that go with it. Usually my whole body is relaxed etc.
Since I've been lying down alot when meditating I've been catching myself snoring (I've been told that I don't usually snore) and sometimes I'm trying to work out where that sound is coming from. Its coming from me lol :-). Also I’ve been having the dreaded “gasps” when lying down. Its when your falling asleep and something forgets to breath and then all of a sudden I’m taking this deep breath and slightly disorientated, and then come back to awareness.
I intend to go back to sitting up as this seems best to minimise the falling asleep or going unconscious.
When I become used to a level the less this unconscious thing seems to happen - meaning that I'm getting used to each level as I progress.
Remember, this is my experience and may not happen to others.
thanks - Lyall