'Alone Again Or' by JY Saville

Franklin lounged across the padded chairs in the mess room, sharing a joke with Halford and Green. They were winding down after a hair-raising moment with an air circulator pump and had left the ship to Harris. It didn't take much running, it had been built for efficiency – a small craft for quick runs between research stations and mining orbitals, though quick could still mean weeks. Long enough for the effects of being cooped up to kick in.

#

Haverah Harris slowed down as he neared the mess room. He could hear voices, though all of them must be Dean Franklin because there was no-one else on board. Telling jokes this time, which was better than arguing with himself; the previous week it had looked like it might come to blows. Try explaining that to head office. Still, probably best to give Dean a wide berth for a while longer; Haverah would prefer it if one of them stayed sane.

#

The room fell silent as they watched Harris slink past the open doorway.

"What's his problem?"

"He's decided we're all figments of his imagination."

"Except me," said Franklin. And laughed.