Gender Dysphoria is not classified as a mental illness by the DSM. Dysphoria means distress, and Gender Dysphoria is a label for the distress that transgender people may experience, not for any supposed mental illness. You could experience dysphoria from a stressful work environment. It wouldn't mean you have a mental illness.
It is important
to note that gender nonconformity is not in itself a mental disorder. The critical element of gender dysphoria
is the presence of clinically significant distress associated with the condition.
