Space happy

From Memory Alpha, the free Star Trek reference

Space happy was an informal term to describe unusual behavior caused by long term space missions.

In 2266, Yeoman Janice Rand suspected that Crewman Green was "space happy" when he displayed strange behavior. In actual fact, Green had been killed and replaced by the M-113 creature, and the creatures behavior was symptomatic of its hunger as it hunted for salt. (TOS: "The Man Trap")