acetylchlodine - a chemical in your brain that makes you dream and that reacts if anything is wrong w you causing several different kinds of ("yikes!") seizures and alzeimers is correlated to the lack of enough of it.

(my poetic intepretation of that is that it's in charge of knowing shit that your conscious mind can't or won't, like memories in your fault/vault and/or that your horse is gonna die.)