Mania describes a state where a person has elevated mood, arousal or energy levels, or they have elevated irritation. They are unusually alert, animated, talkative, and tend to be in a controlled but constant state of movement. It is a symptom of many conditions.
The most usual cause of mania is the use of stimulants, usually cocaine or methamphetamines, but can even occur with caffeine. It is a common side effect of several medications, most notably steroids and SSRIs. However, in the absence of these, it most commonly indicates bipolar disorder.
On House, M.D., Alvie typifies a patient in the manic phase of bipolar disorder - talkative, constantly in motion (particularly his hands), with few or no social inhibitions. However, Alvie's failure to come up with rhymes during the talent show indicates the other side of the disorder - an inflated sense of one's own abilities that can lead to risk-taking behavior.
Alvie's mania was rather mild, but in severe cases it can lead to hallucinations, suspicousness, delusions of grandeur, catatonia and aggressive behavior. It can often lead to a manic patient focussing so much on thoughts and schemes that they neglect their own care. However, many manic patients find that they can be more creative in this state (see as an example Fletcher Stone) and often fight efforts to treat them even when mania alternates with depression.
Mania is a pathology when it continues for more than seven days. One episode of this type is sufficient to establish at least a diagnosis of bipolar disorder. When combined with psychosis, Schizoaffective disorder is a more likely diagnosis.
Mania can be managed with medication, but this requires establishing a diagnosis.