I don’t know about breathing specifically in relation to thyroid function, but I know that, as a yoga teacher/therapist, that chest or thoracic breathing has a correlation to the sympathetic nervous system or flight/fight, while diaphragmatic or belly breathing has a correlation to the parasympathetic nervous system or rest and digest. Likewise an inhalation is linked to sympathetic function while an outbreath is linked to parasympathetic function. So to help get you more chilled try diaphragmatic breathing with an active, long and slow exhalation. I can only assume that if the parasympathetic nervous system is more engaged then energy will be more thyroid based than adrenal based. A few minutes of this breathing every so often through the day may make quite a big difference.