I can post about this now because a few days have passed and Fitz is totally fine and not dead.
I had the day off on Friday and went over to Mr. Kiwi, where I bought, among other things, a gigantic brownie that I planned to share with Devon and a friend later that night. I came downstairs from folding the laundry to find half a brownie and a very guilty-looking 7-pound dog.
I don't know what I expected -- probably for her to drop dead right on top of the brownie. So I IM'd Devon and told him I'd probably killed his dog, and he was pretty nice about the whole thing, and all I could think about was the ferret-in-the-dishwasher incident with his ex-wife, and wondered whether he was wondering why these crazy bitches keep killing his pets, and I realized I should never have children because I couldn't keep a dog alive for three months and I should get a tubal immediately -- or even give myself a tubal because it would be faster than trying to convince a doctor to sterilize a 30-year-old woman with no children and oh, shit, I can't, because the knives are in the sink with all the other dirty dishes I haven't washed yet because I suck, and Fitz, you're a pain in the ass, but you're harmless and sweet, so please don't die.
I managed to squeeze all that in while I Googled vets in Brooklyn. One told me to bring her in, but not to him, because he was closing in 40 minutes. He gave me the number for another vet, who told me to call the ASPCA Animal Poison Control hotline, which wanted to charge me $60 just to tell me whether I should bring her to a vet or not. In the meantime, Devon found a vet nearby who, after making sure there was no pot in the brownies, told him she'd be fine and to keep an eye on her for signs of toxicity, like hyperactivity and vomitting.
So I spent the rest of the day carrying her with me up and down the stairs so I wouldn't miss anything, which probably pissed her off, but that's what she gets for eating chocolate and making me think she was going to die. She spent the rest of the day sleeping.
So Fitz and I have come to an understanding. I agree to let her be her neurotic, crazy-ass self, and she agrees not to catch the death.