I had something like that happen at my last job. One day there was a major fire causing a lot of air pollution. It was so bad that a co-worker had to ask to skip the meeting to take care of her son who has asthma. I have serious respiratory problems, so I considered saying I wasn't going to the meeting because of it. However, the owner has anger management issues, so I went so he wouldn't get mad at me.

It was summer so we had the windows open overnight and were woken up at around 3 AM due to the smoke. After that I couldn't sleep. So, I was tired and generally feeling like garbage from walking to the meeting in the polluted air. I explained this at the start, so he wouldn't get annoyed. Even so, about half an hour in, he sneered at me and said. "you look tired, I hope I'm not boring you". What an ***. So again, I explained how I had felt badly and hadn't slept well because of the fire. Still, he gave me dirty looks for the rest of the meeting.

I agree with the suggestions to bring a glass of water and take some notes to keep yourself more alert. Also, now that you know people have an eye on you, you know to remind yourself to look like you are paying attention. Also maybe going outside for some fresh air right before the meeting can help. It often helps me.