Catherine Zeta Jones |
In depression, there are unipolar and bipolar disorders. With unipolar you only go to one end of the spectrum.
But bipolar takes you to both ends, with stages of being very low and then times of extreme mania.
In essence, you're bouncing from one extreme to another. In extreme cases you might assume a person's being psychotic when in fact they're actually going through a manic stage.
For a lot of people, it's cyclical. For one half of the year they'll feel low, then high for the other half.
Sources: http://www.mirror.co.uk