Hi David,
there are some good points made in this
old thread. I particularly like Duncan's take on it:
Duncan Barford:
I've found it helpful simply to let sensations arise and note them, and if sometimes I fall asleep then so be it - that was my state of mind, and that's what happened. My attention was eroded by sleep. Big deal! I'm a human being! Occasionally, it's possible to sit through a sleepy spell, noting as much as possible, and then discover that the mind becomes alert again after a time. (Presumably because it has simply taken the sleep it needed, and now is more able to continue.) In these cases, techniques to counteract sleepiness might have actually prolonged it.
Refraining from aversion to sleepiness, I've found, letting it take its course (within reason) naturally builds an ability to cope with it over time. I find now that I'm able to remain alert in states of consciousness very close to sleep, sometimes to the point of even having dreams begin to arise without being dragged into them.
Having said that, though, I've recently been practising samatha more frequently, and have found Alan Wallace's advice useful on switching to more subtle objects or sensations when laxity sits in - as counterintuitive as this may seem!
Cheers,
Florian