Insomnia

Insomnia - The inability to difficulty sleeping, can be caused by many things including stress, sickness, and can often be a symptom of underlying disorders.

Insomnia can be classified as transient, acute, or chronic.
Transient insomnia lasts for less than a week. It can be caused by another disorder, by changes in the sleep environment, by the timing of sleep, severe depression, or by stress. Its consequences - sleepiness and impaired psychomotor performance - are similar to those of sleep deprivation.[8]
Acute insomnia is the inability to consistently sleep well for a period of less than a month.
Chronic insomnia lasts for longer than a month. It can be caused by another disorder, or it can be a primary disorder. Its effects can vary according to its causes. They might include muscular fatigue, hallucinations, and/or mental fatigue; but people with chronic insomnia often show increased alertness.[citation needed] Some people that live with this disorder see things as if they are happening in slow motion, wherein moving objects seem to blend together. Can cause double vision.