A 43-year-old female presents with altered mental status.  Her husband states she has had weight gain, constipation, fatigue, and skin changes. Vital signs include BP 92/60, HR 48, T 93.2 rectal, RR 13, SpO2 96% on room air. She is alert and oriented x 1, and her neck reveals a well-healed midline anterior neck scar. Her abdomen is soft but distended, and her extremities are cool. What’s the likely diagnosis?