“Clues”
Just as the Enterprise is going to investigate a mysterious planet, the ship falls into a wormhole and the crew except for Data is rendered unconscious. The whole incident lasted only thirty seconds according to Data, but soon it is suspected that it must have been more than a day - supported by evidence like plants that have grown more than they should and a recent fracture in Worf’s wrist. Is Data lying? Picard orders a course to the planet again, and as the ship arrives, a Paxan occupies Deanna’s body to speak for them. The xenophobic Paxans want to avoid any contact with other civilizations. They usually render every ship crew unconscious and alter computer data and course which didn’t work because Data was immune. They were about to destroy the Enterprise, but Picard ordered Data to be silent about the Paxans at any cost, and they did their best to eliminate all evidence. Picard asks the Paxans to try it again, and they are even more careful this time not to leave anything that needs investigation. Only Data knows about the Paxans. summary by Ex-Astris-Scientia
BRILLIANT AMAZING! ADORABLE! FASCINATING!!!!!!!!!
Ugh… sorry 
Guess I got a little carried away. But it’s not without reasons. THIS is precisely what I love about TNG. Ahh, the mistery! If only I could forget the episode and watch it fresh over and over again! 
Honestly, I realize that time loops and memory losses are not everyone’s favourite plot devices. Me, I just love ‘em. What I remember most vividly from this one is the scene with Doctor Beverly cutting out dry leaves from that plant in her quarters. I must have dreamt about it. Together with “Remember Me” I guess these are my absolute favourites for the whole Star Trek.