Has it been awhile since your previous entry level ground defense class? If it has maybe you just need to get re-conditioned for it. For me personally I work out 6 days a week and I run hill sprints once per week as well as interval running once per week. But when I started playing full court basketball again I was gassed relatively quick even though I felt like I would be in better basketball shape. (I haven't played full court basketball for over a year at this point) After a few more full court basketball sessions though it became easier. I follow a really strict paleo lifestyle as well not because of weight issues but because I had bad allergies which it helped me control. One thing you may consider is if you are going to teach a class maybe have a little bit more carbs pre-workout.
"If man made it, don't eat it" - Jack Lallane
People say I am on a "crazy" diet. What is so crazy about eating veggies, fruits, seafood and organ meats? Just because I don't eat whole wheat and processed food doesn't make my diet "crazy". Maybe everyone else with a SAD are the "crazy" ones for putting that junk in their system.