"O Sleep, O Gentle Sleep.
It has been considered that the playwright's clear descriptions of insomnia suggest that he himself suffered from this malady
Natures self nurse, how have I freighted thee,
That thou no more will weigh my eyelids down
And sleep my senses in forgetfulness."- Shakespeare
Insomnia means getting insufficient sleep which can be in the form of difficulty in falling asleep or difficulty in maintaing sleep. Insomnia is just a symptom, like fever, and is not a disease by itself. Diseases that can disturb sleep, like pain or anxiety usually cause insomnia.
Everyone goes through occasional phases of insomnia which resolves once the causative factor has been dealt with. Problems arise if insomnia continues to persist which can have deleterious effects on one's health. Inadequate sleep can cause daytime sleepiness, which can affect one's productivity at work and may also increase the chances of motor vehicle accidents due to fatigue and impaired concentration.