Altered REM sleep patterns, specifically earlier emergence of REM sleep, are a consistent finding in depression.

“you can say well perhaps that's because Matt you also spoke to me that REM sleep may be important for some aspects of the emotional brain and when you are depressed the brain knows that REM sleep is required and it calls it up on the menu of the series of dishes that you're going to be served earlier on in the night because it's needed more significantly the other and that's the adaptive theory the other is the maladaptive Theory which is that arriving with your REM sleep too early does not do your brain good things and therefore it's some abnormality of emotional processing”

“one of the earliest findings in depression and sleep and has been quite well replicated is a change in REM sleep but now it wasn't necessarily that individuals who had depression slept or had excessive amounts of REM sleep they had a little bit more what was interesting is that when that REM sleep emerged during the night was much earlier”