That can be a sign of several different things. He could have intestinal parasites or fleas that are causing him to be anemic. You can take a stool sample to the vet to have him checked for parasites. You can look him over yourself to check for fleas. Heart problems could have an affect on his gum color if the blood is not circulating like it should. The fact that he is sleeping a lot more than usual along with the pale gums would be a concern to me and I think a vet check would be the safest thing for him. Overweight cats are also prone to being diabetic. Take a look at this link- it could be something as serious as FIA
Feline Leukemia is another possibllity- here is a good link
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