euthymia
noun
eu·thy·mia
| \ yü-ˈthī-mē-ə
\
\
Medical Definition of euthymia
: a normal, tranquil mental state or mood
specifically
: a stable mental state or mood in those affected with bipolar disorder that is neither manic nor depressive
… there were no significant differences among groups in the rates of durable recovery, defined as 8 consecutive weeks of euthymia without a switch to mania or hypomania. — Mark A. Frye, The New England Journal of Medicine, 6 Jan. 2011