Students routinely have anxiety dreams about school--not able to find the right classroom, suddenly recalling a big test coming up. Professors have these dreams too.
In our case, the nightmares are about realizing that we haven't prepared for class, or we've shown up for class seriously underdressed (though fortunately no one has noticed yet), or we can't find the right classroom, or we've been assigned a class we're totally unqualified to teach.
I once dreamed that I discovered, on the first day of school, that the biology department had assigned me to teach a course on the Fungi. In the dream, I was trying to figure out if I could somehow turn the course into Mushrooms in the Middle Ages.
There actually isn't that much to say--not a whole semester's worth, anyway, certainly not what the biology students would have been expecting.
Medieval people certainly gathered and ate mushrooms. These were one of the foods they gathered, rather than growing themselves. (Click here for more on the medieval diet.) For them, as for us, the key point was making sure one did not gather poisonous mushrooms.
This is and was much easier in Europe than in the US, because Europe has far fewer poisonous species. As long as one learns, very carefully and thoroughly, which ones to avoid, the rest are fine. (Though there is a European mushroom that can make you thoroughly drunk after one glass of wine if you eat it with the wine.) In the US, in contrast, almost everything is poisonous, so one has to carefully and thoroughly learn which species are not.
Truffles, then and now, are a highly prized and highly valuable version of mushrooms (or at least fungi). They grow underground on the roots of trees, especially beeches and oaks. Because they are underground, they have to be sniffed out, usually by dogs or pigs. These animals, of course, want to eat them themselves, which can be a problem.