I was able to confirm that Thursday's afterschool in-car distress was most likely due to stomach trouble for two reasons.
Number 1: There were some subtly different changes in Charlie's eating---eating less than he usually does and also requesting to eat a lot---on Thursday. For one thing, after school I had gotten Charlie his usual McDonalds order, two hamburgers and a small Sprite. He routinely takes the burgers apart to eat them (something of a relic of his days on the gluten/casein-free diet, when we always got him 'meat in a box'---a plain hamburger patty), then eats the ketchupy buns with the little pickle slices. Thursday he ate the burgers and only half of one bun.
I didn't realize this till we were home (Charlie had put what he hadn't eaten in the back of the white car while I drove). But I did suspect stomach trouble, possibly, and Jim was well aware of this when he took Charlie on a bike ride. Charlie led him to a shop where he's gotten ice cream in the past, usually two cups. But Thursday, Charlie insisted on four and Jim, seeing as they were in a public place and Charlie had already had one 'neurological storm' (though not world's worst by any measure), followed Charlie's requests. (Still-recent memories of the 'incident of the red brownie box' have taught us, best to do what needs to be done to keep things as calm as they can be in public places, even if it means buying things we'd rather not, within reason.) Jim and Charlie finished the bike ride and Charlie, on coming home, wanted dinner, and then got sick (in the sense of, lost everything he'd just eaten).
And then he was a happy smilin' boy, asking to hear samples from a bunch of albums he usually overlooks and enjoying that final walk with Jim.
Friday Charlie was much more 'his old self' when I picked him up at school (five good days in a row) and as we drove home. I thought of driving home a different direction, but Charlie pointed me to go in the same way and I thought, ok, let's give it a try. I did avoid the radio station with the R & B and went for some snippets of a piano concerto, at a low volume. Other than that, it was the same ride as Thursday, except 100% peaceable. Once home, Charlie brought in all of his own stuff without me asking, and then announced he needed a nap (codeword: 'bedtime'). He slept till 6pm, asked for a bike ride as he got out of bed and went off easy and smooth with Jim. And, indeed 'easy and smooth' went the rest of the day.
Yes, at this point I guess we've gotten pretty attuned to Charlie non-verbally communicating something like stomach distress.
And that Charlie did have some kind of stomach thing was further proved for a Number 2 reason, me finding myself 'indisposed' on Friday, though not to the point that I needed to lie on the couch and have Jim bring me cups of tea or anything like that. If I'm sick during the school year I try to just forge on enough to teach classes and take care of Charlie; getting sick when I don't have to teach classes or drag myself to work coughing, etc. sick and being able to just sit down at home is a real relief. Jim revealed that he'd felt a bit under the weather earlier this week and I found myself feeling, yes, relieved: It's definitely not always the case that we can trace why Charlie gets upset so readily.
I guess so many years of experience---and us being a symbiotic family---helps more than a little, too.