This is from answer.com

"A mixed episode is essentially an episode that simultaneously presents symptoms of both depression and mania. For example, an individual with bipolar disorder (manic depression) may have all the frantic energy of mania, but may also be struggling with the black thoughts of depression. Found here are resources and information regarding this type of episode."

I'm pretty sure I've had a number of mixed episodes and for me they are full of anxiety and wild thoughts.