the only time I've almost fallen asleep at a musical was Shuffle Along. I was thoroughly enjoying the evening but there was a lull in act two with a LOT of dialogue I was having trouble focusing.
i think I fell asleep at a Michigan Opera Theater production a few years ago (I believe it was la rondine or Madama Butterfly in 2008 or so) but only for a few minutes
when I was a teenager I would routinely fall asleep in movie theaters for several minutes, but I attributed that to my poor sleep schedule (staying up too late therefore getting only 4-5 hours of sleep before school) and not on the quality of the film.
"Contentment, it seems, simply happens. It appears accompanied by no bravos and no tears."