Hello ! Thank you for your question, I’m Dr. Vikas (M.D Psychiatry) and I’ll try to help you today.
Bipolar disorder is considered to occur in episodes. As a rough estimate, over patients lifetime, there are 1 or more manic episodes and in almost all patients, also 1 or more depressive episodes are seen.
In between episodes, patients are generally euthymic and free of symptoms with normal mood.
The interval between episodes also varies widely from patient to patient, from as little as weeks to a decade or more. Although in most patients, the intervals are symptoms free and patient remain euthymic (noraml in your words).
In a minority of patients, a mild, residual symptoms may persist in between full-fledged episodes in comparison to other patients who are symptom free during that period.