In mood disorder, rapid cyclers are defined as

(A) 4 or more episodes per year# Rapid cycling:> Most people who meet criteria for bipolar disorder experience a number of episodes, on average 0.4 to 0.7 per year, lasting three to six months.> Rapid cycling, however, is a course specifier that may be applied to any of the above subtypes. It is defined as having four or more episodes per year and is found in a significant fraction of individuals with bipolar disorder. The definition of rapid cycling most frequently cited in the literature (including the DSM) is that of Dunner and Fieve: at least four major depressive, manic, hypomanic or mixed episodes are required to have occurred during a 12-month period.There are references that describe very rapid (ultra-rapid) or extremely rapid (ultra-ultra or ultradian) cycling. One definition of ultra-ultra rapid cycling is defining distinct shifts in mood within a 24-48-hour period.