Outside Practice for November

I went to a Yoga Flow at 9:15 AM on Tuesday. I was having a hard time with my breath work and trying to keep it up for the entire class. I knew something was wrong when I started to black out, see spots and got really cold. I had to sit down on my mat for a few seconds to gain back my equilibrium and make sure that I was able to continue. After about 30 seconds I was good to go again! I really don't know why this happened though. My only guess was that because we kept swan diving then going into forward bend and all the way up again. Also, I had just woke up not too long before I went to class so I dont think my body reacted very well with all of the movements.