.... Usually the Troi-centered episodes of Star Trek: The Next Generation are not the jewels of the franchise but "Night Terrors" is a pretty good episode. Basically, the Enterprise gets caught in a rift in space (the same rift that saw another ship get stuck and its crew gone mad) and can no longer experience REM sleep. This makes the crew become paranoid, hallucinate and get altogether dangerous all except Troi (who is trying to communicate with the other ships' Betazoid to find answers) and Data, who doesn't need sleep.
"Night Terrors" has a thick atmosphere and an effective, creepy mood; featuring some of the most shocking and scary scenes of the entire series (yes, morgues are just as scary in the 24th Century). The ending isn't exactly interesting or thrilling but it's great to see Patrick Stewart, Gates McFadden and Marina Sirtis give some fantastic performances - Brent Spiner in particular gives probably the most interesting performance in the episode with a heartfelt (for Data, anyway) effort.