This article might help explain rapid cycling Bipolar Disorder. I have also copied a portion of that article to this post.

Bipolar Disorder: Rapid Cycling and its Treatment - Depression and Bipolar Support Alliance

What is rapid cycling?

Rapid cycling is defined as four or more manic, hypomanic, or depressive episodes in any 12-month period. With rapid cycling, mood swings can quickly go from low to high and back again, and occur over periods of a few days and sometimes even hours. The person feels like he or she is on a roller coaster, with mood and energy changes that are out-of control and disabling. In some individuals, rapid cycling is characterized by severe irritability, anger, impulsivity, and uncontrollable outbursts. While the term “rapid cycling” may make it sound as if the episodes occur in regular cycles, episodes actually often follow a random pattern. Some patients with rapid cycling appear to experience true manic, mild manic, or depressive episodes that last only for a day. If there are four mood episodes within a month, it is called ultra-rapid cycling, and when several mood switches occur within a day, on several days during one week, it is called ultra-ultra-rapid, or ultradian cycling. Typically, however, someone who experiences such short mood swings has longer episodes as well. Some individuals experience rapid cycling at the beginning of their illness, but for the majority, rapid cycling begins gradually. Most individuals with bipolar disorder, in fact, experience shorter and more frequent episodes over time if their illness is not adequately treated. For most people, rapid cycling is a temporary occurrence. They may experience rapid cycling for a time, then return to a pattern of longer, less frequent episodes, or, in the best case, return to a stabilized mood with the help of treatment. A small number of individuals continue in a rapid cycling pattern indefinitely.