Number the sentences according to their level of generality from 1 to 5 (1 being the most general). The topic sentence is the only sentence that is level 1.

1		Insomnia, which causes people to have trouble falling asleep or staying asleep, is one of the most common types of sleep disorders.
2		Almost everyone has experienced occasional insomnia, also called transient insomnia.
3		This kind of insomnia does not usually require medical intervention.
4		People who experience insomnia fairly regularly, though not constantly, are said to have intermittent insomnia.
5		Both transient and intermittent insomnia are often caused by mental or physical problems, such as pain or worry.
6		They may also be the result of environmental conditions, such as extreme temperatures or noise.
7		When these conditions disappear, the insomnia does too.
8		However, constant insomnia, also known as chronic insomnia, is a much more complex and difficult problem.
9		It can be very disruptive to people's lives, causing continual irritation, tiredness, and an inability to concentrate.
10		It can also be a symptom of a serious medical problem, such as heart failure or kidney disease.
11		For these reasons, people with chronic insomnia are advised to seek medical help.