In times of crisis or emergency, we'll likely be more active as we seek shelter, food, water, and security. Being active and alert for long hours over several days is nothing new for anyone who has served in the military, but may be a challenge for anyone who has lived a moderately sheltered life or works a low-stress job. One of the major problems with being “switched on” for extended periods is the resulting exhaustion and burn-out.
Exhaustion is the result of too much stress, not enough sleep, and/or too much physical activity. There are differing types of exhaustion that I'll break down in my normal manner.
Your body will hit a point of exhaustion if you push it too hard for too long. Strenuous exercise and increased physical activity are likely after an emergency (shoveling snow, clearing downed trees, hiking to your BOL, etc.) and can lead to physical exhaustion. Getting into shape will lessen the impact, but won't eliminate the possibility.
I've stayed awake and on duty for 72 hours at a stretch (when I was much younger), and it took a couple of days for my body to recover. Currently I'm averaging 85 hours a week at my job (harvest season), and after 5 weeks I'm starting to see the signs that my body is reaching its limits: body aches that aren't attributed to physical labor, swollen lymph nodes, a slight depression of my immune systems, decreased appetite, and headaches are all starting to become more common. I need to survive another couple of weeks, and then I'll be able to take a few days off to rest and recuperate. That's the key; being able to sleep and give your body a chance to repair itself is how you recover from physical exhaustion. Downtime is important and needs to be built into any plans for long-term prepping.
Mental exhaustion comes from having to process too much information in too little time. Sleep is needed to process information properly, so lack of sleep will rapidly lead to mental exhaustion. Information overload doesn't only mean too much data coming in; constant noise (or silence for some folks) can have the same mental effects as being bombarded by meaningful data -- it wears on your mind and leads to mental fatigue. Getting away from what stresses you may not be an option in a crisis, but you should try to at least find a way to get a change of scenery on occasion to give your mind a break.
Forgetfulness, distraction, short-term memory loss and self-doubt are all signs of mental exhaustion and should be watched for in yourself and others.
An exhausted spirit is one that has seen or done too much and has shut down. Some spirits are stronger than others, usually due to being exercised by stresses over time, but they can all be burnt out if things get to be too much. Different people have different methods of “recharging” their spirit: music, meditation, writing, talking, and other soothing activities are common methods and may be worth considering when making plans.
Despair, detachment, and an increasingly negative or cynical outlook on things are signs of a person's spirit reaching exhaustion. A broken or exhausted spirit is hard to repair, especially alone, and will take a lot of time to recover if it can. There are a lot of people walking around with exhausted spirits that will never recover, and you likely know a few of them. They're the ones who just don't care any more about anything. They've given up and may never be able to get back to “normal”.
This one is a bit tricky. If you believe in reincarnation or recycling of souls, then the concept of a tired or exhausted soul shouldn't be discarded. A soul that has been around the block too many times without a break will get exhausted and do what it can to get a rest, even if that means starting a new cycle earlier than usual. The realm of the soul is beyond our ability to influence, so you can't really do much to help a worn-out soul. I trust that there is a plan or path for each and every soul and they will make the journey in their own fashion.
Plan to take time for yourself, make sure you have a place to get good sleep (cool, dark, and quiet are the three main ingredients), and do what you can to reduced the physical exertion (get good tools) that you expect to experience. Good nutrition and good company will help with the mental and spiritual stresses, though both may be hard to find. Like most bad things, exhaustion is easier to avoid than recover from.