Ocean Madness

"Don't drink the ocean, K'nuckles! Seawater makes you crazy! Look at me! I've been drinking it for hours!!! NYEHAHAHAHAHAHAHA!"

—Flapjack, The Marvelous Misadventures of Flapjack

Related to Space Madness.

Being away at sea for a long time seems to take its toll on your mind. Maybe it's the unchanging landscape, maybe it's being away from your loved ones. Either way, in period pieces and even sometimes in modern ones, you can expect any characters away on sea for extended periods of time to go crazy.

Historically a Truth in Television. In addition, there's a lot of validity to the "don't drink seawater" idea, since salt water has the nasty effect of making you even more dehydrated, which can lead to delirium. And, y'know, death.

Compare Cabin Fever.

Note that this is no excuse for ocean rudeness.

Examples of Ocean Madness include:

Anime and Manga

Hikari and Ken from Digimon Adventure 02 go mad (or at least have very bad FreakOuts) whenever they return to the Dark Ocean
- Though it's less from the usual reasons, and more because they basically stumbled into a Cosmic Horror Story.
In the Omake episode of Moon Phase, Seiji Mido has gone completely mad from being trapped out at sea for several weeks. Though he could be considered the Only Sane Man, as everyone else is completely blase at their house being intact and floating in the middle of the ocean (the giant cork just has to be left alone).

Film

Results in a particularly delirious musical number in Muppet Treasure Island.

We've got Cabin Fever!
We've lost what sense we had!
We've got Cabin Fever!
We're all going mad!

Arguably, Tom Hanks in Cast Away. He wasn't strictly "at sea", per se, but he fits the rest of the trope.
- On the other hand, what sent him round the twist was probably spending several years with only a (Goddamn) volleyball called Wilson for company rather than being surrounded by ocean.
  - On the yet another hand, Wilson may actually have kept him from going frothing mad by virtue of being "company" to talk to.
Tom Hanks again in Joe vs the Volcano, after days of solitude, dehydration, and exhausting the entertainment potential in his luggage.
Mutiny on the Bounty contains some of this.
An anti-Ocean Madness might be Jack's locker-induced madness at the beginning of Pirates of the Caribbean: At World's End—Hell for a pirate, seemingly, is a barren endless salt flat far from any sea.
- Well, it's definitely Hell for Jack, who has been known to mention that he considers the sea - and having a ship of his own - is one of the few things he actually considers to be worth living for. It's entirely possible that the Locker would appear differently to other people who were trapped in it (as opposed to the rest of the cast, who essentially come into Jack's head).
Master and Commander: The Far Side of the World has a significant subplot concerning an officer who comes to believe he is a curse on the ship. He kills himself.
- His treatment at the hands of the rest of the crew - most of whom shun him - does not help matters. He might not have gone through with it if he'd had any reason to believe that *anyone* on that ship truly believed that he wasn't a Jonah.
  - Jonah, nothing. Put a disturbed, neurotic young man as an officer on a ship where everyone treats him like a pariah and he just got a man flogged for disrespect and you have a recipe for serious depression. His suicide would be understandable even without believing he was personally cursed.
Coffey in The Abyss quickly descends into ocean madness - High Pressure Nervous Syndrome, to be precise.
In The Little Mermaid when Prince Eric wakes up on the beach and starts talking about being rescued by a girl, Grimsby replies, "I think you've swallowed a bit too much seawater."

Literature

The Rime of the Ancient Mariner is essentially about a crazy old man accosting a random guy in the street and making him listen to an extremely gruesome experience of Ocean Madness.
- Hopefully. Because if he was actually sane when he saw all that stuff out there...
  - The fact that the Mariner might be close to a thousand years old would seem to corroborate his story, unless every single detail, including when it happened, is a hallucination.
In China Mieville's The Scar, Hedrigall decides to leave Armada, the floating city, and spends some time alone at sea. After he is found he has been driven mad by seeing his entire city destroyed.
Cryptonomicon has Goto somehow managing to swim all the way from open sea to New Guinea. As an Okinawan who grew up in the sea, he knows damn better than swallowing the sea water. Problem is, he's swimming with a Tokyo city mouse, who doesn't knows any better... and after swallowing the sea water for a while, he slowly starts losing it, until he collapses in the shore while laughing sardonically...
Captain Wolf Larson, in Jack London's novel The Sea Wolf, starts off as a sadistic Nietzsche Wannabe, but degenerates into a full-blown psychopath with a death wish.
From Nation: "Calenture...meant a special kind of madness...sailors got [it] when they'd been becalmed at sea for too long. They'd look over the side and see, instead of the ocean, cool green fields. They'd leap down into them and drown." Although, since it's First Mate Cox doing the explaining there, it's entirely possible that he pushed them in himself.
- Terry Pratchett had already mentioned the phenomenon in Going Postal, where he uses it as an analogy for what happens to clacks operators after a while.
Likely happened to Pi in Life of Pi, becoming most if not all of the conflict in the story.
Inverted in John Masefield's "Sea-Fever":

I must go down to the seas again, to the lonely sea and the sky,
And all I ask is a tall ship and a star to steer her by,
And the wheel's kick and the wind's song and the white sail's shaking,
And a grey mist on the sea's face and a grey dawn breaking.

Live-Action TV

In the TV-movie of Noah's Ark, after the rain ends, the ark drifts for weeks across a sun-drenched and scientifically impossibly dead calm sea, and Noah and his sons and daughters-in-law all gradually go around the bend. However, Noah's wife, being the Mommeee, is supposed to be an infinite source of self-sacrificing nurturance, so when she starts to crack, all the other characters stare at her in shocked amazement and suddenly go sane again.
On Lost the crew of the freighter is slowly going mad while anchored near the Island. However, the main cause is the time-twisting effect of the Island rather than just being at sea.

Tabletop Games

The background for the villain Cannibal from the Dark Champions sourcebook Murder's Row involves him going mad while stranded on the ocean in a lifeboat and discvering he has taste for human flesh...

Western Animation

In The Simpsons, Homer, Bart, Ned and Todd start to succumb to this after they get stranded out at sea in a raft.
The Trope Namer is Futurama, despite this instance actually being a Cassandra Truth. When the crew gets stranded underwater, Fry sees a mermaid, resulting in everyone brushing it off as ocean madness. However, Fry really did see a mermaid, and no one actually goes mad.

Fry: "Everytime something good happens to me you say I have some kind of madness. Or I'm drunk. Or I ate too much candy."
Leela:"It's ocean madness all right, the sailors call it "Aqua Dementia". The deep down crazies, the wet willies, the screaming moist..."

Xavier: Renegade Angel has a variant. (SAAAAAAAND MADNESS!)
Referenced in Road to El Dorado after Miguel, Tulio, and their horse Al Tivo have been floating for God-knows how long and then suddenly wash ashore:

Miguel: And it is! It really is the map to El Dorado! *he pants with excitement*
Tulio: ...you drank the seawater, didn't you?

As quoted, the episode "How the West was Fun" of Flapjack. The full sequence is mildly horrifying