My husband and I adopted two kittens last week (8 weeks old, neutered, have all their shots). They were both so playful and energetic all week, eating their food quickly and taking a small amount of time to sleep during the evening hours when we were around to play with them. During their first weekend with us (when we were both home and free to play), one of the kittens became very lethargic and sleepy, lost interest in playing most of the day, and started to eat less than before. He loves to be petted more than ever now and just wants to sit on my lap, mostly licking my fingers and arms as he relaxes. I do hear him running around a bit while we sleep at night, but his overall activity level has gone down a lot, especially as compared to his brother, who is just as active and hungry as before. Should I worry and / or take him to the vet or this just a case of disturbed and switched sleeping schedules?