His night with a child who could have been -and in some universe was- his son spent tearing down psychic walls and unearthing old memories, time spent with an alternate version of himself, and a conversation with Professor Yana, and Jack had just about had all he couldtake. He was confused, uncertain, and emotionally exhausted.
It was, perhaps, ironic that the place he retreated to was the TARDIS that belonged to the source of a lot of that confusion and exhaustion, but it was still the space he'd claimed as his.
He was on his back on the console room floor, arms splayed on either side of him and looking straight up toward the ceiling. When he heard someone come in he didn't get up, just angled his head back further so he could see.
"Hey," he told the Master. He'd get up in a minute.