The same exact thing happened with my puppies and it made me very nervous, since they had been bundles of energy. I got them at 7 weeks old, and from about 8 weeks - 12 weeks they were very dormant, stayed in bed, slept, rested and ate a smaller amount than I was accustomed to. I could only get them up to play with me for a half hour at a time a few times a day.
They have grown out of that REAL fast though, I assure you.
