Guinea pigs are prey animals and, as such, are cautious little guys. In a new environment, especially alone, it's pretty normal for them to seek cover to help them feel safe and protected. I work from home and can also vouch for the fact that my pigs are up in the morning when the kids are getting ready for school, then lay around (besides occasionally eating and drinking) for much of the day until the kids come home again (at which point they get back up to try to convince the kids to feed them.) Then they are active in the evening for snack time and floor time and then crawl into the pigloo together and go to sleep. So the daily routine of a guinea pig may not be that adventurous, and I don't think it's uncommon that your pig is spending a lot of time not being active. I would also really encourage you to consider a companion pig for him- they really are wired to be social and two guinea pigs are a lot happier and more active than one.