At every meeting, regardess of the time of day, frame of mind, secular workload, etc, I would feel I was being lulled into a numbing sleep.
I just have to weigh in on this... what you said really hit home for me. I always chalked this feeling up to just boredom due to lack of intellectual stimulation. But now I agree that it goes so much farther than that. It is almost like some form of hypnosis. The question and answer format, the repetitive scriptures (there are probably about 100 core scriptures that are constantly being used at the meetings), and the same topics being discussed over and over. If the topic was particularly of interest, I wouldn't get that sleepy feeling, but I know I used to feel it all the time. It almost felt like you were being lulled into a state of complete relaxation.
It is ironic that they stress the importance of the meetings to your spiritual health, because I haven't attended one in 6 months or more, and then decided to go a few weeks back, and its like I have never been gone. There was nothing new or groundbreaking to be observed. I could probably miss 2 years and then go one day only to find they are talking about the same old crap!!
Another interesting phenomenon is when a witness will miss a week or two of meetings, and just feel like something isn't right. I remember experiencing this too. People have even expressed to me that they feel spiritually starving if they miss a few in a row! I guess they like that nice sleepy feeling, and then the subsequent euphoria when the meeting ends