Divers by nature tend to be cucumber cool. How else could you sail out to sea, toss on a tank, and plunge into the depths of the ocean blue? Yet, dwelling within each of us is a panic button that can get pushed when we least expect it, sending us into the danger zone without warning.

Fact is one fifth of all diver deaths can be directly attributed to panic, according to the National Underwater Accident Data Center. Another 22 percent of fatalities remain a mystery. Considering the number of divers who are recovered with working equipment, plenty of air, and their weight belts firmly in place, most experts believe that death due to panic is far more common than reported.

Panic can kill in any number of ways. Rapid, shallow breathing can cause hypoxia and a buildup of carbon dioxide, causing the diver to act irrationally, breathing faster, expelling the regulator or bolting to the surface. These panic responses can make you pass out, or even have a heart attack if you have a weak heart. Panicking also hinders your ability to solve problems and get to safety when your equipment malfunctions. Here’s how to keep your cool.

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Practice makes poised. Always do a checkout dive to make sure your wetsuit still fits (nothing like not being able to breathe to induce anxiety), equipment still works and your skills are sharp. Practice sharing air and clearing your mask and all those skills you may not have done since certification. Know what to do so you problem solve and don’t panic if your regulator starts free flowing or your mask floods or gets kicked off. Review the dive details with the dive master, so there are no surprises. Before a dive, assess your mental state. Ask yourself, "Am I anxious? Am I breathing too fast?" If you answer yes, something about the dive is worrying you. Figure it out and problem-solve it before you go under.

Hatch emergency plans. Stuff happens. It’s rational to be a little afraid when something goes awry underwater, but if you have planned for it that rational fear is far less likely to become irrational panic. What might send you over the edge? Seeing a shark? Losing your dive buddy? Equipment failure? Have an emergency procedure ready for every situation and rehearse them with your dive buddy. That way if something scary happens, you both know what to do and you’ll automatically do it.

Stop. Breathe. Think. Act. Once panic starts creeping in you need to do what you can to stop it in its tracks. It’s nearly impossible to panic when you’re taking deep even breaths from your diaphragm. Train yourself to Stop — Breathe — Think — Act when something unexpected happens. Of course, it's often breathing — specifically the inability to do so — that causes panic. If you're out of air or otherwise having trouble breathing, the other steps still apply. Think about your options. Most people can easily hold their breath for a minute. That's enough time to find your backup air (or buddy) and get a breath.

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Know the signs. The following are classic signs that you're losing your cool (notice that these are signs that you can recognize you before you get in the water, too). If you experience any of them, stop to relax, breathe, think — and seek help.

• Rapid breathing or feeling like you can't get enough air.

• Rapid heart rate, palpitations or heaviness in the chest.

• Gastrointestinal distress, "butterflies," nausea, vomiting or diarrhea.

• Muscle tension, headache or tremors.

• Trembling voice or inability to speak.

• Sweating, chills or hot flashes, feeling out-of-control or impending doom.

Selene Yeager is health and fitness expert and writes regularly about training, fitness, nutrition and health.