A person who has sudden mood swings. That does not mean that they are ALWAYS depressed. Also it means having an alter ego. If it is bad enough you could think that you are two people. If bi-polar was just meant for mood swings then this word would be non-useful. Being bi-polar affects the way you act and think.
keep that in mind kiddos.
I forgot to take my bipolar pills so if i have sudden mood swings please feel free to slap the utter living hell out of me.