I'm 36 years old, I've been around cats for 99% of my life and today is the first time I've seen a cat Panting like a dog.
I totally freaked out, got the cat and used a water spray to spritz cold water over him. Moistened a cool cloth and wiped him down, neither of which made him happy. He shot off, I anxiously googled and it turn s out its perfectly normal. 
The little monkey has been tearing around the house all morning and exhausted himself. 
Two minutes after his panting and my panicking he's happily munching a bit of food and having a drink.