Myxedema coma is a state of decompensated hypothyroidism. A person may have lab values identical to a "normal" hypothyroid state, but a stressful event (such as an infection, myocardial infarction or stroke) precipitates the myxedema coma state, usually in the elderly. Primary symptoms of myxedema coma are altered mental status and low body temperature. Low blood sugar, low blood pressure, hyponatremia, hypercapnia, hypoxia, slowed heart rate, and hypoventilation may also occur.  Myxedema, although included in the name, is not necessarily seen in myxedema coma.
According to newer theories myxedema coma could result from
allostatic overload in a situation were the effects of hypothyroidism are amplified by non-thyroidal illness syndrome. 
References [ edit ]
^ Berghe, edited by Greet van den; Wartofsky, Leonard (2008). Acute endocrinology : from cause to consequence (1 ed.). New York: Humana Press. pp. 29–44. ISBN 978-1-60327-176-9.
^ Chatzitomaris, Apostolos; Hoermann, Rudolf; Midgley, John E.; Hering, Steffen; Urban, Aline; Dietrich, Barbara; Abood, Assjana; Klein, Harald H.; Dietrich, Johannes W. (20 July 2017). "Thyroid Allostasis–Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming". Frontiers in Endocrinology. 8. doi: 10.3389/fendo.2017.00163. PMC . 5517413 PMID 28775711.