Any wild guesses?

Had a puzzling one the other day. Here's the basic facts. I'd be
interested in hearing your speculation on what this gentleman's
problem could have been. 2100 - Wife leaves 40 y.o. husband sleeping
in easy chair in front of TV and goes to bed. 0700 - Wife tries to
wake husband, who is apparently still asleep where she left him last
night. He is unresponsive. We arrive, find husband breathing normally
but unresponsive to command or pain. He is apparently conscious, and
the initial impression is postictal. Generalized muscular rigidity is
noted (posturing?). Pupils dilated, equal, and sluggish. Vitals
unremarkable (BP 140/110, pulse 80 and reg, resp 18). Skin warm, pink,
dry. Lungs clear. Abdomen normal. 2nd exam negative. Wife denies any
medical hx or meds (says he's never been sick a day in his life). She
also vehemently denies possibility of drug abuse (I believe her).
House is normal, clean, middle-class dwelling. He is employed as a vet
at a local animal hospital. No one else in the family had been ill
recently, and everyone had been together and eaten together in the
preceding days. En-route he is NSR on the monitor, blood glucose 89,
O2 sat 98%, pupils remain dilated and sluggish, muscle rigidity
remains. No change in LOC, however he is able to respond with weak
bilateral hand grasps on command (no other motor responses). At the
hospital all bloods work is negative. CT and MRI negative. Basically,
every test in the book is done and every test is negative. He is
admitted to neuro ICU. Later that day his mental status improves
slightly. 24 hrs later CT and MRI still negative, but now his mental
status has improved significantly. 48 hrs after admission CT and MRI
still negative and his mental status has returned to normal. He is
discharged to home with no apparent deficits, no memory of the event,
and no diagnosis. Any wild guesses? Ever see anything like this?