There have been some questions lately about mixed episodes, so I thought I'd cut and paste the description from the National Institute of Health (NIH):

Mixed states

In a full-blown mixed episode, criteria are met for a depressive episode and a manic episode nearly every day for at least 1 week (American Psychiatric Association, 1994). However, a mixture of manic and depressed symptoms may occur without reaching full diagnostic criteria. For example, a patient may have racing thoughts, agitation, overactivity and flight of ideas, but feel worthless, guilty and suicidal. The patients with bipolar I disorder who took part in the 12-year longitudinal study mentioned previously spent an average 6% of weeks in a mixed or cycling state (where polarity of episode was changing and symptoms of both were present) (Judd et al., 2002). For patients with bipolar II disorder the proportion was just over 2% (Judd et al., 2003). It is estimated that approximately two thirds of patients will suffer a mixed episode at some point in their illness (Mackin & Young, 2005). A study of 441 patients with bipolar disorder reported that subclinical mixed episodes are common – with 70% of those in a depressed episode showing clinically significant signs of hypomania and 94% of those with mania or hypomania showing significant depressive symptoms (Bauer et al., 2005). Sub-threshold mixed episodes were more than twice as prevalent as threshold mixed episodes. The combination of morbid, depressed affect with overactivity and racing thoughts makes mixed states a particularly dangerous time for people with bipolar disorder.