My pdoc has used the same description for me. I've also heard 'excited depression'. My last mixed episode landed me in IP.
I'm agitated, I'm impulsive, I have energy, but I'm also suicidal and anxious. I have negative thoughts/ideas, but they come at me with this rush. Like racing thoughts that I can't stop, only they are everything depressive I could ever think. And I can't sleep because of them because it is so loud that I feel like I want to just cover my ears and scream. I often describe it as chaos in my head.
It's hell.