Think before answering this question. If you plan ahead you will not cower but will be able to think clearly and do what is needed and must be done.
Make many plans. Some will not work out. Practice this all the time in all surroundings you find you are in daily.
Boom!???? Been there done that. Lights did not go out. But a plane did explode overhead and rained debris down including body parts and an engine fell on a house right under the exploding plane. Since this was America and we were not under the thumb of a thug regime, we all walked out of our houses to see what had happened. including the family whose home the aircraft jet engine destroyed. They were standing in their front yard as the engine fell on their home and destroyed it. That however it happens is how most of us would react today. Still, my first reaction would be to wait for the shock wave. An EMP explosion probably would be accompanied by a bright enough flash if it is nuclear and be seen by most people for hundreds if not thousands of square miles. Time in that event to activate your plan for that event. If there was no shock wave of appreciable effect, I would assume that it was most likely a transformer as we have had blow near my area several times. No damage, just no power. I would activate the cell phone to call the power company and get a prerecorded message that the power would be back on in a certain amount of time. I would not open my freezers my frozen food will stay frozen for several days if I do not open it. Mine are full all of the time ensuring they will stay frozen longer. It is deer season, any meat will be easily obtained, yes we put away eleven last year. Also squirrels are in abundance as are rabbits and both are good to eat and easily obtained as well.
Under the circumstances, stated plan activations (such as if away from home have a bug out kit with you) or if not and it is something more than lightning, transformer blowout or plane blowing up, maybe even a freight truck loaded with fertilizer such as the one in OK City a few years back or even another truck back in my home town in the late fifties the blew up four city blocks and killed about a dozen folks several of whom were vaporized in the explosion (first responder fire and police). But, and here is the rub, if it is a government action against fellow citizens then katy bar the door, Activate your unit plan, get your phone tree working and move to your pre--planned defensive position. The roads will likely be blocked in strategic spots so plan alternate routes using less well traveled by-ways. Get to your position and stay there as long as necessary taking care to see to it that all access points are covered. Your objective is to stay alive and to protect your family including you team members and their families.
Be advised that the FEMA camps are NOT MYTHS. They do exist and are marked on road signs although most do not know the signs. Google FEMA CAMPS on utube and you will find out how to recognize where you should not go as well as where they will try to take you if you are arrested. If you do not or cannot defend yourselves and your family and are taken, do not resist, do not show a weapon, let them find them and take them because they have already made it clear that they will fire no warning shots. Those of us that plan and will resist will not fire any warning shots either but you need to know they are not your friends if they are acting under orders from Obama. Obama is systematically getting rid of commanders of military units who have voiced opinions that they will not obey his orders to carry out Martial Law orders. Do not think that the military is our friend. Just because we love them and support them does not mean that they will defend us and our freedoms. They may well sit it out or be kept out of the action against their will. Some will join against us. If you doubt that and know your history, you will remember during the Great Depression a large group of Veterans stormed our Congress seeking the wartime bonuses they were promised but never received. They came to Washington to demand their bonuses and the Army was called up and Two of the Most famous General Officers of our History ordered the troops to fire on the veteran protestors which they did. It can happen again make no mistake about that. And do not forget that Obama has sworn in a couple hundred thousand of his so called Civilian Defense Corps supposedly to assist FEMA in carrying out emergency services....they are armed with the same military hardware that the military is. We will have to take those away from them as quickly as possible. That is just my two cents. Also, folks remember we are being monitored and who and what we say is known. Semper Fi.