Have not seen the experience first hand but from a Dom perspective, every minute of your life the external forces acting upon your mental and physical being vary and your reactions to them vary. In forms of exercise, say long distance running, some times one can carry on for hours and miles while another day, the energy is lacking. My personal experience with yoga has me vital and sometimes and totally bored on other occasions. As you could not pinpoint a single incident that sparked your crash, I'd bet it was simply, "one of those things." I'd recommend not dwelling on it or thinking in the future that it will happen again.
Cheers,
Boxer