There is a biorhythm operating 24/7 in our body known as the Basic Rest-Activity Cycle (BRAC). While some biological cycles last for many days, the BRAC oscillates consistently at between 90 and 120 minutes.

Rest portion: During this healing response portion of the cycle, there is more right hemispheric electrical activity, a spatial cognitive mode, and a settling down of the autonomic nervous system. Midway through the rest cycle is a trough of about twenty-minutes. This is when many cells of the brain that hold critical messenger molecules, such as adrenaline, are nearing empty. At this point, all the cells in the body are taking time out to replenish, rejuvenate, and rebalance. It is during this part of the cycle that people daydream, and can be most creative.

Active portion: During this peak performance period of the cycle, there is greater electrical activity in the left hemisphere, a verbal cognitive mode, and the autonomic nervous system is in a phase of sympathetic predominance. This means that it is "open for business." Heightened physical activity, mental alertness, and energy means that logic, rationality, and a black and white approach are being exercised.

People who are continuously over-stimulated do not have the opportunity to recharge their internal batteries. The Central Nervous System, having to contend with the ever-constant activity, will suppress the resting period, resulting in exhaustion in the short-term, and burnout in the long-term.
To better equip a person in dealing with stress, techniques exist to maximize the resources of each side of the brain. An interesting indicator of which side is dominant at any given time, is to simply breathe in through the nostrils. The nostril that draws in the greater amount of air is a contra-lateral indicator of the dominant side. In other words, if the right nostril draws more air, then the left hemisphere is dominant, indicating that the person is presently in the active part of the cycle. One technique to alter the dominance is uni-nostril forced breathing. In this case, to switch dominance to the right, the person would block the right nostril, and force breathing in and out of the left nostril. This would be appropriate if someone wanted the right brain active for a brainstorming exercise or any other creative endeavor.
In the long-term, encourage whole-brain activity through specific kinesthetic activities. Examples are cross-lateral physical exercises, and eye pattern movements. You can also enrich inter-hemispheric communication by using your non-dominant hand to hold a cup, or brush your teeth. Drive a new route to and from work. Experiment with your eyes closed, while dressing, or navigating around your home. Do a blind taste-testing of a beverage.

OK. What about writing a letter or email? Here's a great technique to use if you have no one else to proof-read what you've written. Just wait about 30-45 minutes. Let's say that you wrote it during your active (logical) cycle. By reading it just a bit later, you may be in your rest cycle, when you are naturally more creative. This means you could scan for readability, flow, and sensitivity. Of course, if you wrote it in a creative mind, you would want your logical side checking the details for exactness. How great is that?