Yea, especially given much of the purpose of his flight was to examine the effects of that long in space. I have trouble believing that NASA didn't, if nothing else, give him a phone # to call right away if he had any unexpected symptoms. The whole "should I go to the emergency room" thing kinda seems like a narrative added after the fact to add excitement to his article/book.
(not that I doubt the episode was scary, but I do doubt the fact that NASA would've left any uncertainty about what to do in such a situation)
They have on-call flight surgeon(physicians) for the Astronaut Office. This includes post-mission support.
The narrative seems like it was slightly dramatic to support the story. Similar "unusual" symptoms have occurred on previous missions with other astronauts.
Also, being a senior astronaut, he is likely personal friends with at least one of the assigned flight surgeon.
He's probably picked up a heck of a lot of expertise on basic medical stuff over the years so he can almost be his own CNA.
They probably decided that having him at home in a normal environment with a fitbit or something logging his heart rate and whatnot was better than having him in an unfamiliar hospital.
(not that I doubt the episode was scary, but I do doubt the fact that NASA would've left any uncertainty about what to do in such a situation)