"It's very easy to speculate that the same mind control that you use to control your heart when you're scared also can be called upon to control the other organs in the body. And maybe that's how Wim Hof does this," said Kamler. "It's speculation, but it sort of makes sense, and a lot of scientists are working very hard to try to figure this out now."
On the other end of the spectrum from Hof are those with a condition known as cold urticaria -- quite literally, an allergy to cold temperatures.
"If you put an ice cube on somebody that has cold urticaria, they're going to have a big welt right where the ice cube was," said Dr. Thomas Casale, chief of allergy and immunology at Creighton University and executive vice president of the American Academy of Allergy, Asthma and Immunology.
Worse, those with the condition can expect to experience similar reactions to bitter winds and cold surfaces.
A minor exposure, such as taking a few snowflakes to the face during a blizzard, can result in the formation of itchy, uncomfortable bumps. A major exposure -- such as from diving into a chilly swimming pool -- could theoretically be enough to send the body into a potentially deadly allergic shock.
"There are patients that we've been talking to who have had full-blown vascular collapse and ended up in the emergency room at death's door," said Dr. Gerald Gleich of the University of Utah, who studies patients who suffer from cold urticaria. "This is a very, very potentially serious problem."
Gleich said that as with other allergies, the hives that occur in those with the condition are brought about by an inappropriate immune response. Specifically, an antibody known as immunoglobulin E is likely to blame, as Gleich's studies have revealed that it is this component of the immune system that is activated when these patients encounter a cold stimulus.
Fortunately, this feature of the condition may also point to possibilities for treatment.
"Many of these patients are taking antihistamines, and some are getting good relief," he said. "We would like to see whether antibodies to immunoglobulin E would block all symptoms in these people. If it does, the FDA [Food and Drug Administration] might be willing to approve it and then we would have a treatment."
While nightmares are most often associated with sleep, for a few the inability to get any sleep is a nightmare in and of itself.
Such is the case with 4-year-old Rhett Lamb, who, according to his mother, stays awake nearly 24 hours a day.
"We went to the doctor after he was born, and I kept telling him something was wrong. He didn't sleep," Rhett's mother, Shannon Lamb, told ABC News' "Good Morning America."
"They thought I was being kind of an anxious mom, and we went back and forth," she said. "Finally, they [were] starting to realize now that he really doesn't sleep at all. But we've had a lot of different diagnoses and nobody really knows."
After a number of conflicting opinions, Rhett's parents finally learned what was wrong with their child: Doctors diagnosed Rhett with an extremely rare condition called chiari malformation.