Sudden changes in mood or personality, visual hallucinations and alternations in smell, taste or tactile senses could signal a brain tumor or other abnormality.

WSJ: Confusing Medical Ailments With Mental Illness

Willful, flirtatious and feisty, Katie is prone to mercurial mood changes that result in outbursts of impatient anger, fear or sudden realization, as she struggles to make decisions and find her purpose in life.

WSJ: Review: Mint has a subtle revival of 'Katie Roche'

That's the music you hear during scene changes which serves as a transition from one mood to another or one location to another.

NPR: Barenaked Ladies Meet Shakespeare