Some of these are a stretch, but get at what you describe in which a crew member is not themselves.
S1: The Naked Now: Crew experiences symptoms similar to alcohol intoxication
S1: Datalore. Data is deactivated, and Lore replaces him
S1: The Battle. Picard influenced by Bok
S1: Hide and Q. Riker given Q abilities
S2: The Schizoid Man. Data acts as Dr. Graves.
S2: Unnatural Selection. Pulaski becomes old.
S2: Time Squared. Picard negatively influenced by time travel.
S2: Shades of Gray. Riker poisoned into a coma.
S3: The Price. Troi telepathically influenced by Ral.
S3: Yesterday's Enterprise. The crew was in a different timeline thus acting differently
S3: Allegiance. Picard replaced while real Picard is kidnapped
S3: Hollow Pursuits: Crew is replicated in Barclay's holodeck simulations
S3: Sarek: Picard gets Sarek's mind from a mind meld
S3: The Best of Both Worlds 1. Picard as Locutus.
S4: The Best of Both Worlds 2. Picard as Locutus.
S4: Brothers. Data controlled by Soong to return.
S4: Remember Me. Crew forget that they existed, except for Crusher
S4: Future Imperfect. Crew acting strangely in Riker's simulation
S4: The Loss. Troi loses powers
S4: Clues. Data acting suspicious and lying to the crew about missing day.
S4: Night Terrors. Troi has nightmares about hydrogen atoms
S4: Identify crisis. Geordi transforms into a creature.
S4: Nth Degree. Barclay enhanced by Cytherians
S4: The Mind's Eye. Georgi brainwashed by Romulans.
S5: The Game. Crew except Wesley and Judd controlled by the game.
S5: Violations. Troi telepathically molested
S5: Conundrum: Crew's memories erased
S5: Power Play: Data, Troi, O'Brien controlled by spirits
S5: The Inner Light: Picard becomes another person in simulation
S6: Time's Arrow: Crew must act as 19th century SF citizens.
S6: Man of the People: Troi influenced by psychic ambassador
S6: Rascals. Picard, Keiko, Ro, Guinan transform into children
S6: A Fistful of Datas: Data is a bunch of holodeck old west characters
S6: Face of the enemy: Troi become a Romulan
S6: Tapestry: Picard becomes his younger self with Q
S6: Frame of Mind. Riker finds himself prisoner in an alien mental institution
S6: Decent1/2: Lore controls Data
S7: Gambit 1/2: Picard and Riker masquerade as mercenaries
S7: Phantasms Data has weird dreams
S7: Thine Own Self: Data loses memory, is named Jaden
S7: Masks: Data controlled and speaks as various characters from old civilization
S7: Genesis: Crew de-evolve
S7: All Good Things: Picard moves through time periods by Q
Here are some are not the main crew or main plot, but close to what you describe:
S1: Conspiracy. Parasite entity controls Admiral Quinn and Remmick.
S2: Contagion. Data damaged by computer virus.
S3: Evolution. Data controlled by nanites.
S3: The Most Toys: Data is deactivated to be captured
S3: Deja Q: Q loses his powers
S4: The Host: Riker controlled by Trill Odan (kindof)