Reality star Kendra Wilkinson quit the ABC diving competition show "Splash!" unexpectedly this week, citing acrophobia, a fear of heights, which kept her from completing a dive from a 23-foot-high diving board.

Most of us don't subject ourselves to high-dives nearly as often as contestants on "Splash," but acrophobia is a relatively common fear. Wilkinson, a 27-year-old former Playboy model, merely had the misfortune of having her fear of heights exposed on a national stage.

"I'm so sorry, everybody," the 27-year-old Wilkinson said on the show after her refusal to dive. "It's bittersweet. One thing I don't do is quit. This is the first time in my life I've quit something. This will haunt me for the rest of my life."

Phobias are overwhelming and sometimes debilitating fears of specific objects or situations, causing uncontrollable anxiety and even panic attacks even when they don't present much real danger. It's still unclear what causes them, but a study of people with clinically diagnosed acrophobia found that most patients claimed that they had a fear of heights for as long as they could remember, or developed it as a result of some specific traumatic event.

Phobias don't always require treatment, but a number of therapies exist for people whose specific fears are so severe that they interfere with daily life.

The most widely accepted treatments for extreme phobias are behavior therapies like repeated, prolonged exposure to the source of the phobia with a clinician, or cognitive behavioral therapy (CBT), which involves reframing negative thought processes about the source of the phobia. Some clinicians even use virtual reality exposure therapy to simulate patients' fear of heights without overwhelming them.

Evolutionary theories suggest that a low level of acrophobia is a normal reaction to heights. After all, falling from a high place is a direct threat to survival. Growing infants quickly learn to avoid drop-offs in height, and a low dose of acrophobia is helpful when walking on a cliff, or crossing a bridge with low guardrails.

It's unlikely that Kendra Wilkinson's acrophobia is severe enough to warrant therapy- unless elevated surfaces give her anxiety attacks in daily life, she probably just has a garden variety fear of heights.

I have no disappointment in myself. I did what I could n that was that. Diving is just not my thing n I found that out throughout the show.

— Kendra Wilkinson (@KendraWilkinson) April 3, 2013

Wilkinson explained to E! News how her fear of heights manifests once she gets to the top of a diving platform: "No joke, I start spinning. I start wanting to throw up. I'm shaking. My fingers wiggle. It's like a real thing, when my fingers wiggle-that's, like, a truth."

If she does feel the need for prolonged exposure therapy for acrophobia, she would do well to consult a licensed psychologist instead of "Splash!" judge and Olympic diving gold medalist Greg Louganis. As she undoubtedly learned this week, millions of television viewers are not the ideal audience for facing one's fears.