Here's the line that struck me:
Fernandez went on medical leave in October so doctors could perform emergency surgery to remove a blood clot on the surface of her brain. She officially returned to work in November and appeared at a series of events in December.
Brain surgery in October
Returned to work in November/December
Disappeared in January.
I'm not surprised. The brain is more sensitive than we know. In March 2012 my husband had a benign meningioma removed from the lining of his brain (the meninges). He was back at work by the middle of April, but began to get insomnia and many other symptoms so that by August he could barely function. Luckily, through some combination of drugs and the brain repairing itself and who knows what else, he got through it. Was the hypothalamus, and left temporal lobe "tickled" during the surgery. Maybe.