Zzzzz..........
I have the habit of sleeping late (usually after midnight) and waking up early (usually about 7.30AM). This results in loads of sleepyness during the day, especially when I'm teaching. Oops! ;p
One afternoon (which is my sleepy-est part of the day) some time ago, while one of my students was playing a piece of music to me on the piano, I stood behind her to look at her score, and also to prevent myself from falling asleep (I fall asleep easily while seated). Halfway through the piece, I stumbled and nearly fell over her. That was when I opened my eyes and quickly steadied myself. That was also when I realised I had fallen asleep while standing!
There was also another time (also in the afternoon), I was listening to a student playing scales when I suddenly found myself at a clinic, in front of a doctor. He was prescribing some pills and vitamins for me. Then out of nowhere, somebody asked me something and I replied with a loud "Vitamin C!". That woke me up and I realized that I had been dreaming about the clinic scene. That "somebody asked me something" was actually my student asking me which scale would I like her to play next, and I had said "Vitamin C" instead of "C Major"! No wonder she gave me a funny look!
Nowadays, I still subconsciously fall asleep but I'm trying very hard to keep myself awake by eating sweets and drinking lots of tea, though the latter doesn't work at all for me. The only effective remedy is for me to sleep early, something which I have to discipline myself to do so.