Feeling less strong in hot weather

Over the last few weeks temperatures have gone up to 35C+ here and I have been finding it a real struggle to keep up with my fitness blender program. Generally I feel much more lethargic, But also the videos that I have done in several times before in previous rounds of the program are suddenly much harder and I feel like I have had enough without doing the extra credit classess.

I don't really know if it is the heat or maybe I have just gotten lazy? Does anyone else feel much less motivated or weaker when it gets hot? What is the solution?