Is depression a big cause of insomnia?

Depressed patients complain of insomnia in 90% of cases at some point.  Early morning awakenings are seen in unipolar depression and hyper somnia (over sleepiness) is seen in Bipolar depression most commonly.  50% of sleep studies perfomred on patients with depression show abnormalities including increase sleep onset latency and decreased overall REM sleep and slow wave (deep sleep) and fatigue.

Yes, depression and insomnia often coexist. Often, insomnia precedes the depression and may persist after the depression has been treated. Insomnia is a risk factor for depression.