(CNN) — Most of us are happy with being flung around in a roller coaster or spun high in a Ferris wheel. The rush of fear and the brief re-acquaintance with breakfast are part of the thrill.
But when does a theme park ride stop being scarily fun and start being just plain scary?
We're talking about the rides on which the fear turns into the kind of pure psychological terror that only weeks of counseling -- or a night of martinis -- can resolve.
The rides on which it's not just breakfast that flashes before your eyes, but your entire life (plus some diced carrots that you have no recollection of eating).
These are the scariest theme park rides on Earth. Thankfully, we don't have to try them, because Stefan Zwanzger, aka the globetrotting Theme Park Guy, already has.
And lived to tell the tale.
The rusty roller coasters of Pyongyang (North Korea)
Just when life in a totalitarian state couldn't get any more terrifying, North Korea unleashes some creaking fairground rides on its unsuspecting citizenry.
To be fair, the Kaeson Youth Park is a rare attempt to sprinkle genuine joy on the gray Stalinist cityscape of Pyongyang.
The fear here, says Zwanzger, is an emotional response in no way soothed by geopolitics.
"When you visit North Korea you naturally never feel completely safe and relaxed, so you enter the rides wondering if they've been maintained at all since most were built decades ago.
"The cobwebs aren't a good sign."
Zwanzger's fear-free alternative: Kaeson has a relatively new, Italian-made Zamperla coaster. (Kaeson Youth Park, Kaeson, Pyongyang)
Baku's gross ghost train (Azerbaijan)
For genuinely fun thrills and screams, the Kaeson Youth Park has a relatively new, Italian-made Zamperla coaster.
Most ghost trains are so lame that it's interesting to hear of one that actually does spook its passengers.
Unfortunately, at the time of Zwanzger's visit, this boardwalk ride on Baku's Caspian seafront was getting its screams the lazy way: via pain.
"Imagine you're alone in a ghost train, driving through the dark, and all of a sudden a sticky curtain drops on you from above and sticks itself to your nose and teeth," Zwanzger says.
"And while the ghost train keeps moving forward, the curtain and your nose and teeth don't.
Zwanzger says he complained to the operator.
"Due to the language barrier and the lack of any internationally recognized sign language for 'my nose got stuck to a curtain,' I don't think he got the message. I don't think he really cared about anything, either."
He adds: "Man, that was painful! My love and pity goes out to those who ride it next."
Zwanzger's fear-free alternative: The ghost train at Indonesia's Trans Studio Makassar. (Jalan. H.M Dg. Patompo, Metro Tanjung Bunga, Makassar, Sulawesi Selatan, Indonesia; +62 411 8117000)
The Tehran neck cracker (Iran)
At Iran's Eram Park, it's a tossup between which is more disturbing.
The badly drawn Mickey Mouse cartoons, or the soda can roller coaster?
For Zwanzger, the coaster -- which plays fast and loose with physics by flinging passengers in a such a tight loop they can almost see the backs of their own heads -- wins.
"When I saw this the first time, with Coke can-shaped cars hurtling noisily around a narrow loop, I thought, that's going to hurt.
"And it did. Two to three hours of neck pain followed.
"This roller coaster makes one of the narrowest loopings known to mankind. It's as if your head stays in the same place while the coaster spins around."
Zwanzger's fear-free alternative: Skip roller Iran's coasters altogether and enjoy the country and its wonderful people.
Ferris wheel of misfortune (Nepal)
Take an ordinary Ferris wheel. Fill it with starry-eyed couples and happy families. Then crank the speed dial up to 11. That's how they do it in Nepal.
Because maybe when you live on the slopes of the Himalayas, gaining a few extra meters in height just isn't thrilling enough.
"That thing had speed," says Zwanzger, who says he didn't board the wheel in Kathmandu's Fun Park because the line was too long -- and he was afraid of being propelled into orbit.
"You could hear screams. And these were not the normal Ferris wheel screams of 'ooooh, let's take a photo.'
"These were more like 'argghhh, let me down, I wanna get outta here' screams."
Zwanzger's fear-free alternative: The London Eye (South Bank, London; +44 871 781 3000)
Qingdao chairoplane of pain (China)
Chairoplanes are called chairoplanes because, as with chairs, it's possible to sit in them, and as with planes, all logic says these things should not leave the ground.
Typically chairoplanes rise a few meters off the ground, giving passengers a thrill as they ride in a chair or model aircraft attached by chains to a rotating overhead gantry.
At Fantawild, a new theme park in the Chinese coastal city of Qingdao, the chairoplane ride is less chair, more plane, lofting startled passengers up to almost cruising altitude.
"I was the only rider, and once up in the air, the chains were making creaking and groaning noises and my chair was turning wildly on its own axis," says Zwanzger.
"It was a long ride. And cold. It was new so maybe my fear was just psychological, but I'd rather fly a plane from the 1970s than get back in that Qingdao chairoplane."
Zwanzger's fear-free alternative: Any chairoplane in a European theme park with a budget of more than 100 million euros.
Disney's secret weapon (Various locations)
There is of course, nothing remotely scary about a kid-compatible classic that takes passengers on a mini-tour of a world populated by friendly animatronic puppets.
And yet, says Zwanzger, Disneyland's "It's a Small World" ride, as seen in its U.S., French, Japanese and Hong Kong parks, has untapped potential as a psychological weapon.
"One ride is fun, but try it about six or seven times and it becomes one of the scariest rides on Earth.
"You ask yourself, 'what if I was trapped here listening to that song and seeing these puppets forever?'
"If you were to chain someone in this ride and have them go around over and over, I think it would actually break them."
Zwanzger's fear-free alternative: Disneyland's Big Thunder Mountain Railroad roller coaster should banish the Small World terrors. (Frontierland, Disneyland Resort, 1313 S. Disneyland Dr., Anaheim, California)
The Cannonball Loop (United States, closed)
Like many unnecessary things assembled in the 1980s -- among them the Cadillac Cimarron and mid-career films of Sylvester Stallone -- the Cannonball Loop must've seemed like a good idea at the time.
Looking back, however, it's hard not to view it as the work of an unhinged mind.
The Cannonball was a giant water tube that sent riders sliding through a full 360-degree loop. (See it in action in this YouTube video at 8.19: http://youtu.be/vDHqfhyCbbM)
It enjoyed a brief life in the summer of 1985 at the now-defunct Action Park in Vernon, New Jersey, before being shut down in 1996, reportedly after a series of accidents.
"I've been to almost 300 theme and water parks now, but this is by far the scariest thing I've ever seen," says Zwanzger.
"Looking at it, it's just so obvious that if you have one wrong move, you're going to experience a lot of pain or get trapped inside.
"I can't believe this was actually built in the United States, the country where you can be sued by anyone for just about anything."
Zwanzger's fear-free alternative: Liwa loop at Yas Waterworld (Yas Island, Abu Dhabi; +971 2 414 2000)