Don't worry...enjoy. Once your hamster has become an adult (after about a year), he/she has a few "wild" episodes, but basically settles down. I'm really enjoying mine now that the childhood stuff is over. He's much calmer, and less excited about things--perfectly healthy. Just more mature.
He might have found a chemical or swallowed something while he was out. If you think so, check and see if there is a vet that will see hamsters in your area.
It also could be that he was active at first because of all the excitement of a new place, but now he has gotten used to his environment. Hamsters are nocturnal so most of his activity is at night when your family is asleep.
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