Hi Phantom,
If you're doing guided meditations, they may be taking you too far out of your body. Like awakentransform says, you may be becomming ungrounded. If too much of your energy is pulled out of your physical body and into the spiritual plane, you are going to get very, very sleepy.
By the way, this is one of those things to be wary of. There is no separation between the physical and spiritual planes. We don't have to leave our bodies behind in any way, shape or form. Ideally, when we meditate, we don't have to "go" anywhere.
Some guided meditations are great to get us in touch with different aspects and realms within ourselves, but often they are presented as "going somewhere." That's not a problem either - I've written lots of guided meditations that take the listener elsewhere. But we have to remember that it's all right here, in the present, accessible right from where we are.
So just check in and see if you're "going" somewhere excessively while meditating. You might want to try just focusing on your breath for five minutes at a time, and make that your daily practice for a while. By using a physical function as a focus tool, you are anchoring yourself into the physical plane while meditating.
Blessings,
Andrea
Soul Realignment:Professional Intuitive Development