Fear is an emotion we all experience at one time or another, and its effects are important to understand when talking about disasters. As soon as you feel fear, the amygdala (a small almond-shaped organ in the center of your brain) sends signals to your autonomic nervous system (ANS), which then has a wide range of effects. The ANS kicks in, and suddenly, your heart rate increases, your blood pressure goes up, your breathing gets quicker, and stress hormones such as adrenaline and cortisol are released. The blood flows away from the heart and out towards the extremities, preparing the arms and legs for action. These effects served us well millennia ago, in situations where we were faced with beastly animals that thought they had found dinner.
In modern times, however, bodily responses to fear can be detrimental, especially since the most important one is a negative one: the brain basically shuts down as the body prepares for action. The cerebral cortex, the brain's center for reasoning and judgment, is the area that becomes impaired when the amygdala senses fear. The ability to think and reason decreases as time goes on, so thinking about the next best move in a crisis can be a hard thing to do. Some people even experience feelings of time slowing down, tunnel vision, or feeling like what is happening is not real. These dissociative symptoms can make it hard to stay grounded and logical in a dangerous situation. Essentially, the body's response to fear or stress can be stressful in itself.
Wow, since most situations require us to think first, and then act, the body's response of preparing itself for action while shutting down the brain is not a good thing! So how can we gain better control over our own physiological responses in disasters? The best advice is this: learn to breathe. Yep, this may sound like an odd statement, but gaining conscious control over your breathing is the best thing you can do for yourself. Practice deep, even, controlled breathing when you aren't scared, and you'll be prepared to breathe this way when you do feel scared. Slow, even breathing helps to slow down your heart rate and lower your emotional arousal level. It can also make you feel more like you are in control of the situation, which can help block some of the effects of stress.
In addition to deep breathing, meditation is another thing that people can practice in preparation of dealing with a disaster. Studies show that people who meditate daily have a thicker brain tissue in the prefrontal cortex, which is a part of the brain that handles working memory, attention, and emotion regulation. In short, if you want to get prepared to deal with your body's response to a disaster situation, practice breathing, meditate daily, and be confident in your ability to deal with the tough stuff! Good luck!