Sick Kitty (or is it "Psych!"?)

On Wednesday night, when the heavens broke open and caused all roads to anywhere to be closed out of our town, our cat started acting 'funny'.
And by 'funny', I mean she wasn't eating, using the bathroom or being her usual obnoxious self... and that is unusual for her. Oh, but she was vomiting. Everywhere.

So Hotness (who stresses about this quite easily) was up for most of the night worrying.
The next morning, she was on the phone with the vet making an appointment, hoping they were in as the nearest emergency vet was beyond reach due to the flooding.

She got her in and they did some X-rays to she if had a blockage (i.e. a hairball or somesuch).
They ran some bloodtests to see if she had some exotic disease.
Nothing. They couldn't find anything.
She was a bit dehydrated, but throwing up all night will have that effect on anyone, so no surprise there.

She stayed there all day so they could keep an eye on her, and decided it might be best to keep her overnight for observation.

The next day, she was doing better.
They had given her an I.V. with fluids, she was eating and she had used the bathroom like a normal kitty.
They also gave her a antibiotic as a precaution.
But still no idea what caused the mysterious symptoms of the night before.

We got her home, and after roaming around to make sure we hadn't moved or changed anything, she settled back in.
She ate her food and slept on her petting pad that night.

Other than not using the bathroom that often, she's back to normal. As normal as she gets anyway.

She's old. About 14 or 15 years old. So she isn't a young kitten that can bounce right back.
She's also been with Hotness longer than I have, so Hotness takes it a lot harder when the cat gets like this.

I don't know what to do. I just hope things don't stay on a rollercoaster ride of good one day / bad the next.