The short version: The doctor's visit helped. Medication + blood test + rollback to all-liquid diet have had a dramatic effect (though it's a bit too early to tell if it will last). The presence of kadyg (details), as well as reader sympathy, were tremendous morale boosts. Take me out of the "broken, bedridden, exhausted" column and move me to "jerry-rigged, ambulatory, tired."
Blood test showed nothing wrong; the cynics may collect their wagers.
I've been lying around the house all day again -- but it's been a liberating sort of lying down. I spent most of today in bed by choice (well -- on doctor's recommendation), not because it was a battle to roll out of bed and plod to the kitchen. A good night's rest has eliminated the horizontal-too-long vertigo (ever had that? When you lie down for an hour, but aren't at all sleepy, your brain starts thinking it's upright and then your head swims when you get up? ... If you're in bed all day, this becomes more or less constant). Also gone: The constant muscle fatigue from trying to arrange pillows and a wall into something resembling a chair.
Credit goes, in about equal quantities, to the medication and to Kady's return home.
I've got plenty of experience with loperamide. It's miraculous stuff, and during my hike it singlehandedly helped me limp on through giardia. However, I've also been afraid to take it since this whole gut thing started, because back at the very beginning, I downed a tab of it and spent that night shitting blood.
In hindsight, that was probably due to the diarrhea's cause cause being C.diff. Slowing down gut motion is not a good thing when your body is frantically trying to flush out damaging toxins.
Naturally, without having a good diagnosis for my current woes, I really didn't want to risk that again. Fortunately, the doctor's handholding and discussion of the difference in symptoms was enough to change my mind. (The accountability issue was certainly one factor: "Hey, doc, the thing you told me to do, as opposed to my own dumbfuckery, now has me shitting blood. AARRRGH AMERICAN HEALTH CARE!")
To be honest, though ... this didn't feel like c.diff, and it is a pathetic testament to my state of medical affairs that I am able to distinguish between at least three different diarrheal causes based purely on texture.* (Maybe I should take my first visit to a Third World country and expand my repertoire?) And it turned out not to be infectious, anyway; the blood test showed no elevated white cell counts.
That narrows this particular attack down to either a food intolerance, or else (as roaminrob suggested, and which is starting to bear serious examination) some body issue such as IBS-PI. I'm already working on an elimination diet to rule out the former; once my gut stabilizes I'm also going to schedule an appointment for an occult blood test to rule out anything more serious.
At any rate, Kady's visit provided the other half of last night's recovery. She came home from cooking school and missed a day of cooking class in order to ... cook all evening; she made -- from scratch! -- chicken broth and beef consomme and some apple gelatin (i.e., not from a box ending in "-O"). The doctor had ordered me to regress to a clear-liquids-only diet, and all I had in the house was water and Gatorade; Kady's visit allowed me to actually have some variety. And calories. Ohhhh, yes, important calories.
I don't know what my exact weight was before this started on Sunday, but when I weighed in at the doctor's office I was at 183, which I figure to be about a 5 percent drop (and at least two waist inches) in 48 hours. (And that's after partially compensating for Sunday's dehydration.) I've been burning reserves continuously since this started, and I'm still going through them now, but at least I'm starting to turn the trend around. A liter bottle of Gatorade's only about 200 calories; I went through that much within about two hours of her return.
So, the bottom line is: It looks like I'm past the worst of this particular bout. Its severity and speed were pretty terrifying, so I'm going to try to take this opportunity to learn how to stave it off again.
I can't afford any more guessing. Savings will cover this one, but between lost wages, doctor's visits, and Kady's trip home, we're out $500.
* Giardia is lumpy (and shocking, happy-face yellow); c.diff. is slimy (and horrible smelling); and the current (and, yes, multiply experienced; just never this severely) OMGFUCKEMPTYTHECOLONNOWitis is something akin to being hit with Spider Jerusalem's gun. Aren't you glad you read the footnote?