There are several operas that work for me, at least when I sit in the
opera house.  I almost always get some micro sleep.

One of those I remember best was Orfeo ed Eurydice at Drottningholm.
There had been much talk of an unusually fast tempo for Che faro so I
waited eagerly.  Suddenly I heard the orchestral music that ends it!
I had fallen asleep.

I think it's quite natural to go to sleep when it gets dark.  Damned Wagner
who got the idea that it should be dark during the performance as the most
important thing was not for the audience to see each other.  But though it
never gets completely dark at Drottningholm I can sleep there too.

Per Baeckstroem