It's hot. If it's not hot, its raining with no warning. You would think rain would bring so cool air, but no, it just makes it even more like a terrarium.
Now, if that doesn't explain why I'm cranky, go outside. Stay there for many hours. Do things that are physically exerting. Drink so much water you should be leaking it out of your eyeballs, but never pee.
Easier would be to have someone breathe on you all day. All day. Except for Monday, when the temperature of the outside air will be higher than the temperature of inside of my body. So maybe have a dragon breathe on you all day. Yes. A dragon.
Now tell me how you feel.