The Naked Time
What would this list be without "The Naked Time"? In the fourth episode of season one, Sulu becomes infected with a mysterious space virus that lowers his inhibitions. Though to us, this virus sounds more like a trip to the local bar than a viral infection. Turns out, when Sulu becomes infected and his inhibitions are lowered, he reveals himself to be a "swashbuckler of the 19th century." After joyfully abandoning his post on the bridge, he gallivants shirtless through the Enterprise corridors wielding a sword. Prior to filming the episode, Takei had no fencing experience.
No doubt about it, this episode is a classic, due in part to Sulu! In this episode, the crew beams down to a planet where alien technology grants you anything you want by reading your thoughts. Apparently, the first thing in Sulu's head was an old-style Colt revolver. As if that wasn't enough, he later conjures up a samurai who attacks him. We're qualifying this as "losing it" because why would such a beautiful planet evoke these violent things in Sulu's head?
The Return of the Archons
This marks the first of many times the crew will be caught up in alien mind control. This time, the crew encounters a society that is totally repressed and buttoned up except for the 12-hour free reign period called The Festival. The episode opens with Sulu being asked by locals to join "the body." Once he joins, he doesn't get to do much except smile unsettlingly, which might be for the best. We can't help but wonder what the sword-wielding and pistol-wishing Sulu would have done during The Festival.
This is perhaps Sulu's greatest moment in Star Trek. We know, we know — it's not really Sulu, but instead an evil and insidious version who exists in the mirror universe. Where do we start with Sulu "losing it" here? Oh, how about his plan to kill the Captain and Spock so he can take the throne of Enterprise commander? This is a dark side of Sulu that is unseen until this episode. Takei's perfomance makes it worth every second.
Guess what happens in this episode? You guessed it — alien mind control. Sulu and Scotty get dragged under the influence of two aliens who are traveling around the galaxy pretending to be a warlock and a sorceress. This episode was originally designed to be a Halloween-themed episode. Although this episode doesn't generally make anyone's list of favorite Trek episodes, it certainly made this one.
And the Children Shall Lead
This plot is silly, containing five children as the only survivors of a distant colony. The kids and their "leader," Gorgan, make the crew see terrifying visions. In one cringeworthy moment, Sulu is frozen by the sight of daggers flying out of space on the bridge viewscreen. Originally intended to mimick a bad drug trip, the episode came out more kooky than scary. But, hey, we'd probably lose it too from time to time if we were surrounded by five children at once.