Primary insomnia is insomnia which does not have a specific medical or emotional root. For example, primary insomnia is insomnia that does not appear as a side-effect of medication or as a symptom of an emotional or medical disorder. In other words primary disorder can be linked directly to its cause and is a primary, rather than a secondary, result of that cause.

A good example of primary insomnia would be insomnia resulting from long-haul air travel. Here it is the shift in your body's internal clock, which is a direct result of air travel, which causes your insomnia. Another good example is shift work insomnia in which you are asking your body to sleep when its internal clock says you should be awake and to work when your clock says you should be sleeping.

Secondary insomnia is often much more complex and can be caused by a whole variety of different things.

A common cause of secondary insomnia is an emotional disorder such as anxiety, depression or post-traumatic stress disorder. Other emotional disorders also giving rise to insomnia as a secondary symptom might include Parkinson's and Alzheimer's diseases.

There are also a number of common medical conditions which can give rise to insomnia including those with accompanying chronic pain, such as arthritis; those which affect breathing, such as asthma or certain heart problems and a range of general conditions including an overactive thyroid, gastrointestinal difficulties and heartburn.

Other sleep problems can themselves also give rise to insomnia and a good example of this would be restless leg syndrome.

Perhaps the commonest cause of secondary insomnia however is seen in the side-effects of a range of medications and in other chemical substances which we put into our bodies.

Medicines used to treat the common cold, asthma, allergies and heart conditions can often lead to insomnia. In addition, alcohol, caffeine and nicotine account for a substantial proportion of people suffering from insomnia.

Perhaps the most surprising cause of secondary insomnia however is to be found in sedatives - the common sleeping pill. Although sleeping pills can be very helpful in the short-term many people continue to take them for extended periods and unwittingly cause rather than cure their insomnia.