What could cause severe depression when waking up in the morning?

I was so depressed this morning it was actually painful . I know I was dreaming about my bff’s husband but surely that alone wouldn’t cause it I don’t think. I’m ok now but for hours I felt that life was just too much of a hassle. I went in my office and closed the door. My s/o was cheerful as usual but I could sense he knew something was wrong. He made me a pancake and a slice of bacon.