The National Institute of Health defines insomnia as, "the perception or complaint of inadequate sleep" and classifies it as three types; transient, intermittent and chronic. Most people have suffered from insomnia at one time or other in its transient (one day to a month) or intermittent (occasional) form. Around 10% of the population suffers from chronic insomnia. Elderly persons, menopausal women and pregnant women are more likely to be more affected than others.

Causes of insomnia are classified into three broad categories - life style, physical health disorders and mental health disorders. Life style can be subdivided into what we eat, sleeping environment and sleep schedule. Alcohol, caffeine, nicotine, some allergic foods and medications like decongestants, bronchodilators, anti hypertensives, anti depressants, diuretics, anti epileptics, anti arrhythmic, thyroid medications and histamine H2 inhibitors are known to cause insomnia.

Environmental noise, extreme temperatures, change of sleeping area, uncomfortable bed and insects like mosquitoes are the main environmental factors that prevent sleep. Varying work schedules like shift work, jet lag, long afternoon naps and recreational activities are also causes that upset a good night's sleep.

Obviously, one cannot fall asleep if in pain due to injury or illness. Sleep specific disorders are obstructive sleep apnea, central sleep apnea, restless leg syndrome, circadian rhythm disorder and periodic limb movement disorder. The diseases that become an underlying cause of insomnia are arthritis, asthma, Parkinson's diseases, hyperthyroid, prostrate problems, degenerative disease, gastro esophageal reflux, fibromyalgia kidney disease, heart failure and rhinitis. Menopause can cause sleep problems due to hormonal imbalance.

Stress, anxiety, grief, depression, schizophrenia, panic disorder and mania and acute psychosis are psychiatric conditions that cause insomnia. Above all, the worry that one is not getting sufficient sleep is likely to worsen the problem. This, in turn, creates a vicious cycle, which can make the condition serious.

The causes of insomnia are very complex and it is very difficult to pin down to a single or even a few causes. A patient study of behavioral pattern, sleep history chart and if required specialized study with polysomnogram and full co-operation of the family is needed to determine the cause of insomnia.