Monday after supper, she began to show a whole bunch of problems, involving several of her systems. A quick call to the hospital and a chat with a clinician, and I took her in. The initial suspicion was an early onset of Addison's disease, a chronic condition of the adrenal glands. She was also dehydrated.
So after some IV fluids, lots of tests, and rest, Sadie was discharged. It is not Addison's, fortunately. The doctors still don't know what was wrong with her, but suspect she may have eaten something toxic in our back yard. (Which is, in some ways, peculiar, as we use no chemicals in our gardening.) I guess this means that I won't be letting Miss Sadie out as freely as in the past. Which is sad for her.
In the meantime, she is getting back to her "normal" self. A bit more rest, and no recurring symptoms, and she'll be just fine. My wallet, on the other hand. . . .