Trouble falling asleep and staying asleep troubles nearly half of all adult Americans. This inability to obtain restorative sleep (insomnia) can be transient, short-term, chronic intermittent or chronic persistent.

• Transient insomnia refers to person's inability to sleep well for several nights. Stress or excitement is the usual trigger. Classic examples include start of school year, new school, before exams or sporting events, before a critical business meeting, after arguments, during travels from home or during illness.
  
  
• Short-term insomnia refers to inability to obtain consistent sleep for 2-3 weeks. On-going stress at work or home is the usual trigger.
  
  
• Chronic intermittent insomnia refers to recurring episodes of transient or short-term insomnia spanning months to years. The episodic occurrences are usually linked with definable episodic stresses.
  
  
• Chronic persistent insomnia refers to inability to sleep restfully on most nights lasting for months to years. More than 35 million Americans are affected. More than half of the cases are due to physical illness and the remaining cases are usually due to environmental, psychological, or lifestyle factors.

The health consequence of non-treatment is severe. The primary treatments for transient, short-term and intermittent insomnia consist of practicing good sleep habits, behavioral modification and cautious use of short acting hypnotics as the last option. For chronic persistent insomnia, an intense evaluation for an underlying physiological or psychological cause must be undertaken and only then can appropriate treatment be considered. The primary causes of chronic persistent insomnia includes sleep apnea syndromes (5-15%), leg movement syndromes (2-5%), neurologic/medical illness (3-5%), delayed sleep phase syndrome (5-10%), mood disorders (30%), anxiety disorder (5-10%), psychophysiologic disorder (10%), poor sleep hygiene (5-10%) and idiopathic (2.5-5%).