Something really similar happened to me on Saturday--while we were up in Salem, I felt out of nowhere like I'd been sandbagged, with all the symptoms you mention plus nausea and splitting headache. We got home about 9pm, and I was asleep on the couch by 9:45. Sunday I felt a bit better, enough to exercise, but Monday was a feat of endurance and today's a little shaky (though I think I'll go to dance class). I didn't think to check my temperature, but it wouldn't surprise me if I had a fever. I was hot out in the living room but hurt in the a/c in the bedroom. So maybe there's some wierd thing going around.