I need some advice from you guys😊

I am doing the FB sweat program, week three now. It has been challenging and fun. However, the last week I have been so tired and exhausted after my workouts, it starts approximately 2 hours after the workout and lasts the rest of the day. This is especially after the HIIT workouts. I feel good during the workouts and directly after. I didn’t have this problem at all with FB Burn earlier this winter. Could the long workouts in FB sweat be too long and hard for me?