They tested this trope on their December 22nd 2010 episode. Their result? Confirmed. While not up to control, all three testers did better in practical tests when frazzled and then slapped than when unslapped. At least when the subject isn't suffering from PTSD, as above. Depends if the subject is already in a situation which can trigger a psychosis episode, it can actually snap them out of it. Largely due to the endorphins that get released from the sudden shock. This is because being slapped activates the flight-or-fight response. PTSD is this response having caused too much stress leading to a mental breakdown, so activating it could actually make it worse.
Even earlier than this episode, they examined this trope in terms of a "sobering up" technique after getting drunk and deemed it plausible. Cue Adam getting slapped by Jamie (Cue to 1:47).
Basil Fawlty becomes hysterical with panic after hiring a cheaper builder against his wife's wishes who botches the hotel's renovations, so Polly smacks him. Apparently, he realized that's what he needed, because he told her to do it again.
In another episode, he has her do it to one of the guests, who freaks out upon seeing Basil and Polly lugging a dead guest around. Polly decks the old woman with one punch.
Hurley does it to Charlie, who is afraid to die due to Desmond's visions, so he can convince Charlie to help him drive a van. Hurley's exact words were:
Hurley: Snap out of it! Stop feelin' sorry for yourself 'cause someone said you're gonna die!
Locke (or rather the smoke monster) does this to Claire in the sixth season when she freaks out over Kate raising Aaron.
Inverted (kinda!) in the third season finale of NCIS as Gibbs regains his composure — and his memories! — when Ziva hits herself with his hand. Gibbs being a fan of the Dope Slap, that's exactly why Ziva's amnesia cure worked — she grabbed Gibbs' wrist and walked him through the Gibbs Slap he delivers to his team members Once an Episode, which helped cue his memories of them.
Spaced. Whenever Tim flashbacks to his relationship with his ex-girlfriend and goes off on a tirade, Mike is expected to slap him in his face. If Mike's not around, Daisy does it.
Used in the 3rd Rock from the Sun episode "Nightmare on Dick Street" when Dick is looped out on antidepressants.
Sally: Dick, exactly what did this psychiatrist do to you? Dick: Well, we chatted a bit and he put everything in order. Oh, by the way, Sally, you're now my daughter. Sally: What? Snap out of it! (slaps Dick) Dick:(a la Chinatown) My sister. (slap) My daughter. (slap) My sister. (slap) My daughter. (slap) My sister and my daughter.
Subverted in the Heroes flashback episode. Angela's heretofore unknown sister starts having a Super Power Meltdown and Dr. Chandra Suresh, Mohinder's father slaps her in an attempt to calm her down. Her father blasts him with a psychic wave, after which the soldiers mow down everybody in the interment camp secret government experiment to study powers sanctuary for specials.
In one episode, Niles convinces himself that he is now a regular, beer-drinking, pool-shooting guy. Only a brotherly slap from Frasier restores him to his Chardonnay-sipping self.
In another episode, Niles returns the favour by slapping Frasier out of his frenzy (after he had gone as far as to suggest they'd go into a restaurant they wouldn't need a reservation for).
In Cheers, when Frasier goes into a jealous rage over Lilith's wedding shower including a male stripper, Sam tosses a drink in his face. Frasier's stunned response: "Creme de menthe? You couldn't have found some water?"
Rawls: You, McNulty, are a gaping asshole. I know it, and I'll be fucked if everybody in CID doesn't know it. But, I'll also be fucked if I let you sit here and think you did a single fucking thing to get a fucking police shot. Believe it or not, not everything is about you. Get it into your head, McNulty — it's not on you... and the motherfucker telling you this, he fucking hates your guts. So you know that if it was your fault, I'd be the first son of a bitch to tell you.
Used in the Seinfeld episode "The Puerto Rican Day", where a parade is obstructing the traffic, and Elaine tries to go through underneath a viewing stand, leading a group of people, but they arrive to a brick wall.
Elaine: Oh, no! I thought— Man: You thought?! We're gonna die in the dark! I knew it! I knew it! We're gonna die! Elaine: Get a hold of yourself! (she slaps him, they start shoving each other, then kiss)
In the Sketch / Skit / Comedy show We Are Klang!, the Ditz of the group runs in thinking his mum's stolen (makes sense in context), and the big guy slaps him and shouts... You know what, this is easier:
Big guy: Calm down! (smacks him) Bearded bloke: Yeah calm down! (hits him with a hammer in the groin) Guy 1: Calm down! Guy 2: Yeah calm down! Guy 1: Calm down! Guy 2: Yeah calm down! Guy 1: Calm down! Guy 2: Yeah calm down! Ditz: I'm calm, I'm calm! Non sequitur person unrelated to the show: HE SAID, CALM DOOOOWN. (smacks him)
In the episode "The Naked Time", Kirk does this to Spock. After several slaps, Spock finally retaliates and sends Kirk flying across the room. It does seem to work though.
He also attempts it on McCoy, under the influence of the Lotus-Eater Machine in "The Return of the Archons". This one isn't so successful.
Star Trek: Deep Space Nine: "The Die is Cast": Just before the ship is destroyed, Garak gets Odo to the runabout but goes back for Tain, who's trapped on the bridge in a state of shock. Garak can't talk sense into him and can't abandon him. Odo has to punch Garak unconscious to get him off the ship. Later, Garak does acknowledge that Odo's action was the only way to bring him to his senses and that it saved his life as a result.
Parodied in an episode where Beth slaps Bill upon news that Mr. James's air balloon has gone down. Bill says, "No, see, I'm supposed to hit you."
In another episode this is parodied when Catherine says this to Bill and then slaps him. Bill complains because he was completely calm at the time and Catherine replies that she believes in preventive medicine. Catherine regularly slaps any of the male characters who annoy her.
Another parody in Blackadder. Baldrick and George are trying frantically to remember who George was supposed to write to, to stop Captain Blackadder's execution, until Baldrick grabs a cricket bat and knocks George over the head with it. George says, "No, it hasn't helped." Then Baldrick says, "No, it has, sir!" as he now remembers.
The Mighty Boosh has a slight running gag where Howar gets too wrapped up in his emotions, for whatever reason, and someone slaps his sober, whether or not they actually had to.
Played straight in Battlestar Galactica: Razor, where after the attack on the Pegasus leaves Kendra Shaw in shock and bleeding on the floor with a probable concussion, Cain whacks her mightily across the face and follows it with a stern, "Get up, soldier." She does, her clarity apparently restored.
In an episode of Night Court, Dan Fielding is freaking out about having inadvertently accepted a bribe; Harry gets him to stop by taking out a water pistol and shooting him.
Used periodically by Eddie in Bottom whenever Richie is freaking out, although the traditional slap on the face is usually replaced by a solid minute of Eddie pummelling Richie around the head with a blunt instrument.
Stargate Atlantis has an episode where Bill Nye (yes, thatBill Nye, playing himself) slaps a guest-star scientist who's freaking out and tells him to "man up!"
When Roger Sterling of Mad Men has a heart attack (nearly going out with a Bang), he keeps mumbling the name of the one-night stand he was with. Don arrives and hears him. Cue Don slapping Roger on the face, growling this:
Jamie does this to Polly in "The Underwater Menace" when she's freaking out about how she can't go into the rising water. Averted in the BBC's audio reconstruction of the episode, which edits it to Jamie roughly pulling her to her feet, as the director and Anneke Wills agreed it was out of character (Jamie's character suffers some Early Installment Weirdness in that story as he had been added to the cast after the script had been written, meaning he spent it speaking lines and doing things intended for other characters).
Gets an amusing gender reversal when Zoe slaps Jamie to snap him out of being paralysed with fear in "The Mind Robber".
One of the more uncomfortable Pertwee-era moments is when the Doctor slaps Jo to snap her out of a screaming fit in "The Claws of Axos".
In "The Horror of Fang Rock", Leela slaps the Screaming Woman Adelaide to snap her out of her hysterics.
Inverted in with "The Big Bang". The Doctor, as part of a Secret Test of Character, tells Auton Rory not to bother with Amy:
The Doctor: Your girlfriend isn't as important as the universe. Rory: She is to me! (Rory punches him) The Doctor: WELCOME BACK, RORY WILLIAMS!
Invoked word for word on Todd and the Book of Pure Evil, when Curtis begins freaking out of their lack of marijuana. He shrieks that getting high allowed him to deal with the horrible things they see every week. Without pot, all the blood and gore they see seems so much more bloody and gory and gut-y...
Todd:(slap) Get a hold of yourself, man!
Played horribly in The Pacific when a Marine has a nightmare in a foxhole one night and begins screaming in terror, which of course could give away their position to the enemy. In desperation, one Marine finally hits him over the head with something, and in the morning they realize that he's dead. Everyone is horrified, especially the one who hit him, but Eugene says it was better him than all of them, and Snafu agrees that it had to be done.
Played for comedy in an episode of The Goodies. Tim is in hysterics. Graeme lightly slaps him. Tim is silent for about two seconds...and then slaps back much harder, sending Graeme tumbling into a nearby pile of boxes.
In Kath and Kim...Kath, Kim and Sharon often slip into moments where two of them scream at each other, while the third breaks up the problem. Almost always it's Kim and Sharon arguing with Kath as the peacemaker, though occasionally Kim will scream on her own, calming down when Sharon slaps her.
Done in a funny way in A.N.T. Farm when their fellow ANT is caught in the wave of passing by high schoolers, Fletcher said that they should save him, only for Olive to say he's gone, complete with a Bright Slap.
Sort of inversion on Black Books, where Bernard pulls a Get a Hold of Yourself, Man! on the stressed-out Manny by grabbing him, shaking him back and forth and hysterically yelling "CALM DOWN! CALM DOWN! CALM DOWN!"
Tokusou Sentai Dekaranger - In one of the earliest episodes, Houji gets depressed over a single mistake. Later when they need to track the Villain of the Week through a computer, Ban finds him just sitting there, idle. When he refuses to do anything, Ban drop-kicks him, and tells him to stop feeling sorry for himself and do something. It works like a charm.
Juken Sentai Gekiranger - Near the end of the first training arc, Rio beats Jan, Ran and Retsu so badly that the mentor has to let himself be taken hostage to save them and give them another chance to fight him. Cue the Rangers sitting in the rain, so demoralized they can't even get up...until Miki smacks all of them, one after the other. Near the end of the series, Jan does this to Rio after the latter learns that his entire life has been manipulated by Long.
Kaizoku Sentai Gokaiger - After Don beats himself up due to not being able to save his friends, Navi comes in and slaps him with his robotic wing. Cue Don going in like a badass, complete with long coat, and saving Marvelous.
Samurai Sentai Shinkenger: - Chiaki delivers one to Takeru to snap the latter out of a Heroic BSOD after it is revealed that Takeru is not actually the head of the Shiba clan and has kept this secret from his teammates the whole time they've known him. Amusingly, Takeru actually dodges the first blow, whereupon Chiaki demands that he hold still before swinging again.
Buffy the Vampire Slayer. When Buffy falls into an Angst Coma after Dawn is taken by Glory, her friends try to talk her out of her comatose state gently. Spike gets annoyed and starts shaking and then punches Buffy. When the other Scoobies object, Spike points out that the Slayer's Made of Iron nature means he doesn't have to be delicate.
In "The Night the Lights Went Out in Vegas", there is a power outage in the entire city, and Mike and Ed are locked up in the surveillance room. Mike, who is claustrophobic, starts freaking out, leading Ed to hit him. Subverted in that Mike says it doesn't work – he's still freaking out, but now his face hurts.
Delinda does it to Mike again in a later episode.
Mike: What is it with your family and hitting people?
The Carol Burnett Show has a running gag in the sketch "Went With the Wind" in which Sissy panics about everything, until Starlet slaps her. Eventually, Sissy slaps herself to calm down. At the end of the sketch, Starlet starts panicking, until Sissy slaps her.
Unsere Mütter, unsere Väter: Friedhelm grabs Wilhelm to tell him to pull himself together after the latter breaks down over the futility of their current mission during the Battle of Kursk (basically, keep advancing down this useless street until your whole unit is dead), because despite everything, they need a commander.
In the Series 2 finale of Mrs. Brown's Boys, a drunk Hillary goes wild when she realises her daughter is going into labour. So Agnes (in "slow motion") slaps her. Then Hillary slaps Agnes. Then Agnes headbutts Hillary!