If you're contented one moment, then sad the next, then angry, then joyous, then irritable, you're suffering from moodiness, or changeable moods.
Artists and poets and other creative types are often noted, fairly or not, for their moodiness. (We sometimes call them "mercurial," which means almost the same thing). But everyone suffers from moodiness every once in a while: teenagers besieged by hormones, toddlers who don't get their way, or anyone suffering from an overload of stress. Sometimes moodiness can also mean "gloominess."
