Insomnia is characterized by an inability to sleep and/or to remain asleep for a reasonable period. Insomniacs typically complain of being unable to close their eyes or "rest their mind" for more than a few minutes at a time. Both organic and nonorganic insomnia constitute a sleep disorder. It is oftenly caused by fear, stress, anxiety, medications, herbs or caffeine. An overactive mind or physical pain may also be a cause. Finding the underlying cause of insomnia is usually necessary to cure it.