Andrus Hagan was a male Betazoid scientific advisor for the 24th century United Federation of Planets. In 2367, he was assigned to work for Starfleet aboard the starship USS Brattain.
When the Brattain fell prey to a Tyken's Rift in 2367, her Human crew eventually went insane and killed each other due to the lack of dreaming. In contrast, he had nightmares he could not control, and therefore got little sleep. The visions he saw were actually telepathic messages from a ship trapped inside the Rift, however, he was not able to understand it or get the crew to take action on it. He became the sole survivor, but almost catatonic.
A few weeks later, an away team from the USS Enterprise-D found Hagan, himself either insane or rendered mute. Hagan was treated in sickbay although Doctor Crusher wasn't able to help him. Troi communicated with him telepathically, but received only information she wasn't able to interpret. With more effort from Hagan, she connected that they were both having the same nightmare, and that it was a message.
Once the Enterprise freed the trapped ship, they were able to move away from the Rift and Hagan recovered. (TNG: "Night Terrors")