I've been stung by those little bastards several times, and never really thought much about it. The worst I ever felt was a little nausea for a couple of hours.
But last night, actually about 1:00 this morning, while I was asleep, one of them crawled up into the bed and stung me. It must have hit a vein or something. After a few minutes, the sting itself had pretty much stopped hurting and I went back to sleep. When I woke up this morning, my lips, tongue, toes, and the bottoms of my feet were all a little numb.
If you've ever donated plasma, you know that tingly feeling you get in your mouth and maybe fingers when the anti-coagulant hits you? It felt like that, but not quite as strong.
It's now 17 hours after the sting, and I still feel a little nauseous. The numbness in my feet went away pretty soon after I woke up, but the weird feeling in my mouth persisted almost all day.
What seems really weird to me about a scorpion sting is that it never leaves a mark on me. If I get stung by a wasp or even a honey bee, there will be localized swelling and redness (and in the case of a red wasp, localized fever and general nausea). I can still feel a little discomfort where this thing got me last night, but if you were to try and find it by looking for it, you would be out of luck. There is just nothing there.