The problem with sleeping is that everyone does it. It's the one habit that no one can give up because it is essential to survival. Sleeping, it self, is not the real problem it is what's accompanied by sleep, which is dreams. Again dreams are not the real problem, because there are good and bad dreams, but even some of the good can be harmful to our emotions. The bad on the other hand relates to disease, the bad being nightmares. The disease is a psychological disorder called post-traumatic stress disorder (PTSD) and occurs often after a traumatic event occurs such as terror incidents, returning from war etc. These dreams often have to be treated with medication or therapy in order for the victim to recuperate.
Dreaming usually occurs during a sleep cycle called rapid eye movement (REM). This particular sleep cycle usually occurs within the first 90 minutes of sleep and normally is the deepest occurring sleep cycle.
Before REM sleep there are four other stages of sleep called non-REM (NREM) sleep. REM is the fifth cycle of sleep that occurs, if you exclude waking. Waking is sometimes considered a cycle of NREM sleep, which would make six cycles of sleep instead of five, with waking being the first cycle.
During our waking hours is usually when our dreams gain the potential to become nightmares. Our nightmares are often based on our emotions and most often include feelings such as anxiety, feelings of rejection or fear from being rejected, anger, guilt, or depression, along with many other things. Our state of mind while asleep and dreaming is called our "unconscious self." It is believed that some nightmares purposes are strictly warnings, meaning that our unconscious self knows something about our future that our waking self does not yet know.