Ataraxia is the freedom from distress or worry in ancient Greek philosophy. However, emotions play a vital role in motivation and decision making. Many disorders relate to having excessive emotional reactions or inappropriate triggers for them. There are also a few concerning a lack of or dulled emotional responses. While high levels of stress and anxiety are seen as harmful, the same concern is rarely shown for the opposite end of the spectrum.
I have been unable to find any information about disorders related to dulled or absent anxiety or stress reactions. I assume this is due to the lower perceived harm, or conflation with depression disorders, but I find it hard to believe no one has done any work in this area. Clinical apathy is not what I'm looking for, since that seems to be typified by acute lack of response or interest in immediate stimulus or short time spans.