Mania describes a condtion characterised by severely elevated mood. Associated with bipolar disorder, where episodes of mania alternate with episodes of depression. (Note: not all mania is bipolar disorder, other diseases can cause mania - however bipolar disorder is the 'classic' manic disease).
Although 'severely elevated mood' sounds pleasant, the actual experience of mania is usually unpleasant and frightening for the person involved.
Other manic symptoms include hypersexuality, religiosity, and hyperactivity.
This has caused speculation amongst doctors that mania and depression are two independent axes in the a bipolar spectrum, rather than opposites.