Hi new user here, urgent question!

Hi. I'm hoping you can help as I'm not sure whats happening.
I have a 10 week old kitten who is a very VERY playful little chap, who loves to eat. I've noticed that all of a sudden all he wants to do is sleep, doesn't drink, and only eats a few bites of food. He miows before he goes to the toilet, and on occasion doesn't go at all. I'm taking him to the vet tomorrow, but in the meantime any ideas? I haven't got a clue whats up, its my first cat and I'm worried!

Many thanks for your help.
Satin Angel.