Violating your inner sleep pattern will not specifically cause mental illness but it will cause mental unwellness and an increased risk of some cancers. This means, if you are a true night hawk, you can get damaged by forcing yourself up early every morning, and if you are a lark, you might fall ill if you always work the night shift.

People are quite programmed with their own type of sleep schedule. That said, getting depressed might make you an owl when you weren't one before. Sometimes the sleep changes actually appear you yourself understand you are heading for a depressive episode.

My nurse used to claim I was making myself depressed because I did not rise at 7 am as was her ideal for her system. I say she was a moron.