Dog suddenly getting up in the middle of the night.

Every few nights, my dog has been getting up in the middle of the night and he looks around at something. Sometimes he just stares at nothing. Sometimes it’s only 10 minutes but it’s lasted to up to an hour. I don’t know if he’s hearing sounds but he’s never done it before. It’s been going on for about 2 weeks. He is 5 years old and we had a vet checkup 2 months ago with no issues.