A 65-year-old woman undergoes a thyroid lobectomy for a follicular neoplasm. She has a history of coronary artery disease, hypertension, insulin-dependent diabetes, and stroke. The procedure lasted 2 hours during which the patient required occasional Neo-Synephrine for brief interoperative hypotension. Two hours after the procedure, the nurse calls from the PACU to report that the patient is agitated and hypertensive. Which of the following is unlikely to be the cause for her agitation?