This is one kind of disorder that is most common. It can be split into two different categories. This may depend on how long it may last. Insomnia that lasts for about a few days is called transient insomnia. Insomnia that lasts for a few weeks is called short term and that which goes on for more than three weeks is called chronic. One other way of classifying insomnia is by the source. The two classifications are primary and secondary.