Brumation?

Hi everyone, a couple times a week my 1.5 year old named Pip has been going into his cave and sleeping the whole day. When he does this, he usually comes back out of the cave the same day and goes back to basking right before his lights turn out, then he just goes back to normal for a few days before he does it again. He has a great appetite, no behavioral changes, and he's still pooping regularly. This is my first winter with him, so I'm thinking this could be a semi-brumation thing? But I'd like a second opinion in case it's time for a vet visit. His basking temp stays around 102F, and his cool side is at 75F. He's under a reptisun 10 T8 tube that I just replaced in November. He gets crickets every morning, 5 days with calcium and 2 days with multivitamin. He also gets a salad w/ collard greens every day, but he rarely ever takes more than a bite out of it. He weighs ~380g. I bathe him 2 times a week, but I also offer him water from a dropper every morning.

It sounds like he's OK and otherwise acting normally so it could just be a seasonal slowdown. Look out for him losing weight or any major appetite changes but otherwise I'd let him do his thing.