The value of unstressing.
Almost all my students have voiced concern over what to do if they fall asleep during meditation. I've kept my answers consistent. If we stay seated, with our back supported and our head and neck free, it is a rare occurrence to actually fall asleep, but it may happen, and it is never a cause for alarm.
The reason we do not lay prone to meditate is this: lying down signals to the body to release sleep chemistry. Sitting with the back supported signals to the practiced meditator that it is time to transcend. If sleep occurs, it might mean that everything is working as it should, and that the phenomenon of stress release is happening.
When stresses unwind that have been stored in the tissues of our bodies, whatever has built up comes out. Sometimes this is exhaustion or sleep deprivation. If I notice my head is cocked at a weird angle, or my mouth is dry, this is usually the explanation. If it happens, I don't fuss; I just add five or ten more minutes to my meditation. If I have run out of time and have to be somewhere, I take note of the fact that I'm currently unstressing sleep deprivation, and that I should allow myself nap time whenever possible.
Regardless of what is happening, I know that I can always call my instructor or attend a knowledge meeting for useful feedback from my teacher and members of the meditation community.
Knowledge meetings and group meditations are recommended to renew and reinvigorate your meditation practice. Please avail yourself of this resource. For my students, there is a knowledge meeting every Sunday at 10:00 am. I answer questions at a group level and privately, then we meditate as a group (an experience not to be missed). There is no charge. All are welcome; even non-meditators can get a benefit and will be given a free technique that will prove helpful. If you're in Los Angeles, let me know if you want to drop by.