Unnoticed by the crew of the USS Brattain and later the USS Enterprise-D in 2367, the being tried to communicate with the crew during their sleep and was responsible for the loss of the REM sleep. Betazoids were able to communicate with this being in their REM phase although the communication attempt was not clear.
The being tried to communicate with Andrus Hagan, the Betazoid science adviser on the Brattain and was thereby inadvertently responsible for the madness and the final death of the crew except Hagan, who was left in a coma like status.
Deanna Troi was able to communicate with this being and discovered that this species was trapped in the Tyken's Rift like the starship crews. With Data's help they've planned an attempt to leave the rift by helping the being to create an explosion. Troi, manually set by Doctor Beverly Crusher into the REM sleep, informed the being that the Enterprise-D will help them and release hydrogen from their Bussard collectors. The being finally appeared as a bright Human silhouette before Troi woke up.
"See the eyes...in the dark! One moon...circles!"
- -Tyken's Rift being describing hydrogen (2367)