Can you tell if your cat is more sleepy than usual or is a bit more lethargic? So, how well do you know your cat? Most pet owners inadvertently are aware of their cats sleep patterns. They probably stay indoors and sleep in a nice warm spot more in the winter but if they are sleeping a lot more and aren’t as responsive and you are worried do contact your vet. However, the average adult cat may spend 16 to 18 hours per day sleeping but will be alert if there is noise or if they are disturbed.