Everyone complains about insomnia. Statistically, women complain more often than men across all age groups. Clearly, there is something about being female, beyond sleeping with snoring partners, which leads to a poor night's sleep. As you will see, the quality of our sleep may be influenced by our genes and diet.
It is currently thought that the first appearance of sleep as we now know it, i.e. a cyclic balance between dreaming and non-dreaming sleep, first appeared in mammals about 150 million years ago. Prior to that, it is believed that there was only non-dreaming sleep; what we now call slow-wave sleep. Since that time, the brain has evolved in many different ways to obtain a good balance between times spent awake or asleep. For example, many seagoing mammals are able to place one hemisphere into deep sleep while the other hemisphere is wide awake. In order to survive, dolphins can never place both sides of their brains into dream sleep. After all, some part of their brain has to be awake to swim to the surface for air. What is so critical about sleep that our brain can justify shutting down consciousness in an entire hemisphere?
Memory formation and destruction is the currently the best proposed explanation for sleep. Since we only have one brain to work with, in order to fully process information gathered throughout the day the brain must be shut down. Dream sleep, or what is called rapid eye-movement sleep, facilitates the use of newly learned information for creative problem solving when you wake up. Scientists have discovered that it is not the quantity of sleep, but the quality (i.e., a balance of slow-wave and rapid eye-movement) sleep that improves your memory. If we do not respect this balance we place ourselves at greater risk for obesity, depression, anxiety, heart disease, high blood pressure, impaired immune function, increased joint inflammation, and a higher incidence of metabolic syndrome leading to insulin insensitivity and diabetes. In addition, humans and other mammals that sleep more hours per night on average have more white blood cells and fewer infections. The right amount of the different sleep stages is critical for good health.