[Hamsterita]

If he's eating, drinking, pooing and weeing normally I would't be very concerned.

Some hams are lazy, others just don't enjoy human contact. Maybe at the beginning he was settling and that's why he was more hyper, he was exploring everything, marking it, and being curious. Maybe he's still setting. Anyway, I've read that syrians usually don't get up in the day. Mine doesn't come out til 2 am. Maybe he is being more active at night too and sleeping the rest of the time.