Yes I have dozed off many times when I used to attend. Most of the time kept the shades on as we used to have outside assemblies. The thing was not to slide off the chair, drop your head forward or snore.
I've seen some brothers/sister hitting a serious lean to the left or right as they slept and then they'd jerk awake, only to lean again.
Some people had sneaky methods. My cousin, while sleeping would turn the pages of the bible. Some would lower there umbrellas so low that you couldn't see what was happening under there.
At the very last assembly I went too - I literally laid out a blanket on the lawn and unashamadly caught a 2 talk sleep.