It very well could be from sickness. Sickness takes a toll on your body and wears you down, that could cause you to fall asleep easily. Mabey changing the time of day you meditate while ill could help.

I've also found that when I lay down instead of sitting for meditation I drift in and out of sleep.

You mentioned some insomnia in another post, so maybe you are just tired, Jai. And after all, your body has a job to do, too...healing. My advice is to let it be OK, and it will pass when you are feeling better.

This is exactly what's supposed to happen, if your body needs sleep.

When you meditate, you slip into alpha and theta brainwaves. Theta is that grey line between sleep and wakefulness, so once you begin visualizing things (an indicator that you are in theta), you're only one step away from delta sleep.

If you find yourself falling asleep while meditating, just begin your meditation again after you wake up and your body no longer craves sleep.

Looks like you found a cure for your insomnia.

In sickness, sleep is far more beneficial to your soul than meditation. When you reach deep sleep your soul is re-charging your spiritual batteries. So sleep and enjoy your sleep without any guilt.

Jai, don't take problem by this impediment to meditate; it isn't a problem. Say "Thank you" to Divine for tou can sleeping and joy. You just surpassed a very stressing period. Let your body to replenish with energies and balance them. Be sure your Soul and Spirit alloved this.Remember: the Universe works for your highest good!, even if your mind tells other.

I also use the meditation-prayer just before sleep, laying. Many times I planify the awakening hour (For awakening with a clear, good feeling state, it must be a multiple of a sleep cycle's duration = one hour and 1/2, aproximately 90 mins. This mean: 1&1/2; 3; 4&1/2; 6; 7&1/2 hours). Going from meditation into sleeping, with your permission, is a very pleasant and peacefull feeling.

And, how Vesuvius says, meditate with task after sleeping.

Health and blessings, Gleam

Meditation is very relaxing, it can be done from laying down or sitting or standing such as in yoga in some pose. The body has a natural tendency to want to sleep when it gets very relaxed. Also times of meditation such as meditating before sleep may not be as advantageous as meditating after sleep. Or as well meditation can be done during a bright time when you feel most aware and awake for some this would be around noon.

It would not be as good right after a big lunch as your stomach would be full and it is not as easy to relax but maybe (like for swimming) a half hour after eating would be fine.

Try changing the time or position for example with position, meditating sitting in a chair or cross legged or even in a zen posture with feet under. As I think of your knee problem a chair meditation would be as much as you could stand but keep your back straight and head up also if you keep your hands in front of you in namaste position it is harder to fall asleep since you will feel your hands dropping.