How many hours has that been? How has he been feeling prior to today and has he been going to the litter box regularly??
If it is just since this morning, give the little guy a chance to get the day started, but if this has been an issue before today, and he has not used his litter box, then I would suggest he see the vet.
Kittens are usually pretty active, but they also require a lot of sleep. It could be nothing, then again if this continues it could be something serious that needs medical attention.
Just know that a kitten will get very dehydrated, very quickly without eating or drinking. If nothing else he may be in need of IV fluids for rehydration.
Get back to us , and let us know what is happening, K?
Others here may have better answers. If you are VERY worried, well you know your kit better than anyone, and he should see the vet or vet emergency ASAP.
How is the baby doing? Please let us know .