Different people have a separate sleeping schedule and need different amounts of sleep. A lack of sleep is known as insomnia, which is defined as the quality of your sleep and how you feel after sleeping. It does depend on the number of hours you sleep or how quickly you doze off. You can feel tired and fatigued during the day, even if you?re spending eight hours a night. Sleep disorders are conditions that impair a person?s ability to get healthy, restorative sleep. There are various possible reasons for these conditions, and they are variable and range from practices people have acquired before going to sleep. It also varies by several medical problems that upset the normal sleep cycle. If you notice you have a pattern of not feeling rested in the mornings after you wake up, you should probably see your doctor determine if you have a sleep disorder.