This sleep disorder can be acute, or short-term, or chronic, lasting weeks or months. It can be linked to an outside cause, such as stress, medicine, or a medical condition. When insomnia is the result of an outside cause, it is called secondary insomnia. Primary insomnia is not caused by outside events. It can be hard to identify the cause of primary insomnia.
Here is more information about some types of insomnia:
Psycho-physiological insomnia occurs when someone under emotional stress becomes anxious, concentrates too intently on trying to sleep, and is unable to sleep because of the level of stress and anxiety.
Paradoxical insomnia, formerly known as sleep-state misperception, is a sleep disorder characterized by a significant difference between the time a person thinks he or she has been asleep and how much time he or she has actually slept. People with this problem may complain that they can't fall asleep and feel sleepy during the day because of lack of sleep, but they are actually sleeping and have no evidence of a sleep disorder.