According to Osho, do not feel guilty: falling asleep in discourse is natural and even spiritual. Let it happen totally. It may be ordinary sleep from night-time deficiency that will soon balance, or it may be yoga nidra—meditative sleep—where relaxation deepens and you still absorb the transmission. Don’t resist, don’t make commandments; acceptance allows both rest and inner growth.
It’s okay to doze off—relax, your body may need rest, and you can still receive the teaching while sleepy.