Lunch time workout

My spin teacher, Jennifer, recently started teaching a noon body conditioning class on Thursdays. I went last week and thought it was a great workout.
So I went back today. For some reason everyone was kinda sluggish in class, myself included. I coulda taken a nap during abs just about anytime.
Once back at work I had lunch. That perked me up a bit. And then a diet Dr. Pepper helped a little.
I am wondering if allergies are just keeping me exhausted. Or just that I am super busy at work, stuff to do at home, etc.