According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) primary insomnia is defined as a complaint of difficulty initiating and/or maintaining sleep or a non-restorative sleep for at least 1 month.
The definition of an international sleep medicine organization (Classification of Sleep Disorders-Revised ICSD-R) describes the term "psycho-physiological insomnia" as severe impairment of sleep with decreased functioning during wakefulness. Any sleep impairment longer than 6 month is regarded as a chronic problem.
Insomnia has to be differentiated from
- circadian rhythm disorder (sleep periods or duration is not according the local clock or usual time)
- parasomnias (behavioural events like sleepwalking or night terrors interfere with restorative sleep)
- secondary insomnia (medical and psychiatric problems are the source of the sleep problems.
To evaluate the degree of impairment you have to consider the daytime consequences of the problem. Usually insomnia will cause fatigue during the day, with loss of concentration or trouble focusing on tasks. Sleep problems can also have an influence on the mood or psychosomatic complains like hypertension. We know that different factors can contribute to insomnia including psychological issues or psychiatric disorders, environmental factors, stress or medical disorders. Alcohol and even some drugs can also cause chronic sleeping problems.
Short periods with disturbed sleep for a night or two usually do not cause any severe problems. But if it affects daily functions and lasts for weeks, months or even years you should consider professional help.