Bubonic Plague

We had a scare the other night that Eric likes to think was caused by the bubonic plague. We stayed at his sister's house over the Easter weekend and Saturday night were watching a movie. I went to bed early and when E finally came down he was moaning in pain, his stomach was killing him. I was worried but fell back asleep, after he so kindly told me to "stop worrying and go back to sleep." :) Next thing I knew it was early morning and he was getting back into our make shift bed complaining about his tongue.
"Jody, my tongue is black." Half, okay 1/4 awake I looked at his tongue and sure enough it was black. I don't remember it being ultra black, but he was super worried so he went and brushed his teeth and the black gunk came right off. So what caused it? Chewable tums. We researched online and people taking these before bed was a common factor in waking up with a black tongue. We're just grateful he wasn't bitton ;) by a rat or something to acquire this nasty disease.