Uuh, I find great relief upon finding this..... Because I just did the same thing. I only got my Braces on a couple of months ago, and they gave me all this stuff to take home- Including some of these lovely tablets.
Upon being handed said stuff, they mentioned tablets that help you see the bits you need to clean off of your teeth, so naturally, as an intelligent 16 year old (.......) I thought these were said thing. .... Naturally, I put it in my mouth, though as I was at home, I was lucky enough to be able to just go running into the bathroom to spit the horrid thing into the toilet, and bring up the glass of orange juice I'd previously consumed. I'm pretty sure I didn't swallow any of it, and the first thing I did after that horrid ordeal, was to google it, naturally, to make sure I wasn't about to die.
As I said, I found great relief when I came across this post. I'm pretty confident now that I'm not going to drop dead, and that's always a good thing. So you're not alone!! :')