ICD-10 criteria

http://www.fortunecity.com/campus/psychology/781/icd.htm
"F30.0 Hypomania

Hypomania is a lesser degree of mania, in which abnormalities of mood and behaviour are too persistent and marked to be included under cyclothymia but are not accompanied by hallucinations or delusions. There is a persistent mild elevation of mood (for at least several days on end), increased energy and activity, and usually marked feelings of well-being and both physical and mental efficiency. Increased sociability, talkativeness, overfamiliarity, increased sexual energy, and a decreased need for sleep are often present but not to the extent that they lead to severe disruption of work or result in social rejection. Irritability, conceit, and boorish behaviour may take the place of the more usual euphoric sociability.

Concentration and attention may be impaired, thus diminishing the ability to settle down to work or to relaxation and leisure, but this may not prevent the appearance of interests in quite new ventures and activities, or mild over-spending.

Diagnostic Guidelines

Several of the features mentioned above, consistent with elevated or changed mood and increased activity, should be present for at least several days on end, to a degree and with a persistence greater than described for cyclothymia. Considerable interference with work or social activity is consistent with a diagnosis of hypomania, but if disruption of these is severe or complete, mania should be diagnosed."

http://www.fortunecity.com/campus/psychology/781/cycloicd.htm

"F34.0 Cyclothymia

A persistent instability of mood, involving numerous periods of mild depression and mild elation. This instability usually develops early in adult life and pursues a chronic course, although at times the mood may be normal and stable for months at a time. The mood swings are usually perceived by the individual as being unrelated to life events. The diagnosis is difficult to establish without a prolonged period of observation or an unusually good account of the individual's past behaviour. Because the mood swings are relatively mild and the periods of mood elevation may be enjoyable, cyclothymia frequently fails to come to medical attention. In some cases this may be because the mood change, although present, is less prominent than cyclical changes in activity, self-confidence, sociability, or appetitive behaviour. If required, age of onset may be specified as early (in late teenage or the twenties) or late.

Diagnostic Guidelines

The essential feature is a persistent instability of mood, involving numerous periods of mild depression and mild elation, none of which has been sufficiently severe or prolonged to fulfil the criteria for bipolar affective disorder or recurrent depressive disorder. This implies that individual episodes of mood swings do not fulfil the criteria for any of the categories described under manic episode or depressive episode."