It is a hot vinyasa flow - and I felt too droopy to go to the AM class this morning, so I went to a class later that afternoon that was 90 minutes of heated, flowing poses.
I had more energy leaving the class then I did going in. I feel freaking great! I'll take it day by day, but I think my body wants to work hard while fasting, to keep the energy there. And yoga isn't really work - it's fun and healthy. :-)