At the convention my head would always nod. Unfortunately, there was no head rest so no way of falling asleep there. Plus your mum or whoever was next to you would wake you up.
It's simply not possible to listen to talk after talk after talk for 8 hours and stay sharp. The brain doesn't learn that way. Listening and watching WILL make you tired after 1.5 hours even if you're 100% interested. Unfortunately the GB haven't read "worldly" psychology that tells them that people learn more and retain more in 20 minute bursts with a short break between each one.