Actually if I'm not mistaken, its called ultradian cycling, mixed would be experiencing symptoms of both depression and hypomania simultaneously.

And yes I too have experienced it so it definitely is possible. Mine was due to cold turkeying my meds, I would wake up hopelessly suicidal, even out and be baseline by lunch time and then be gloriously hypomanic in the evening. most exhausting and confusing 3 months of my life.