TLDR: Young hognose, only 15grams, hasn't been seen or eaten in over a week. When should I start to worry?

I've had my young hoggie since labor day weekend in September. Up until this past week, I'd see him regularly, sometimes he's out before I go to work but I would always see him out and about on the weekends. On November 5th, I took him out to handle like I do every weekend, and I weighed him (15 grams). I put him back, he when into one of his burrows, and I haven't seen him since. I was originally telling myself it's okay, they can do this and be fine, but now I'm starting to worry. Is it possible he's brumating? We've had the windows open with the cooler weather, but his tank hasn't gotten cooler than 70 degrees F in the day time (that I've seen) and he has a heat mat that goes to 90 degrees F at nighttime (I have the heat sensor right where the mat is so it only gets to 90 right at the mat, under the substrate). Is this still in the normal range of behavior?