Most people in the world have had mood swings in their lives. A "mixed state" of bipolar disorder generally requires that symptoms be severe enough (and usually long enough) to qualify as some episode. The traditional definition of an episode with mixed features is one where some or many symptoms of both depression and hypomania (or mania) happen simultaneously or in rapid succession.

Moodswings of milder intensity are often more common in people with bipolar disorder than the general public, from what I've learned from my psychiatrist and past therapist.