I'm a new hedgehog owner as well but I can tell you about my similar experience. My little guy was very active the day we brought him home and the day after but then his activity dropped. I took him to the vet. He had mites which may or may not have played a role in his decreased activity but what I noticed about his room was there were nights when my daughter slept with her tv on. I start having her turn it off and his activity has increased. Good luck!