Not quite a mixed state. I don't know what to call it. I experience the same phenomenon... I'm fine at work, but as soon as I get home, I hate life... My therapist thinks it's just a matter of distraction - I can't wallow at work the way I do at home... but that's a different topic.

In a mixed state, a person has very high energy and a very low mood at the same time, not alternating. Have you ever been depressed but extremely restless? That's more what it would be like.

(FYI - although I haven't ever experienced a mixed state, I have witnessed it in my patients as part of my medical training. I saw a few cases while I was doing my clinical rotation in psychiatry... Mixed states are not nearly as common as mania or depression.)