Today I completely forgot a word. It's when you find out or realize the truth about a person or situation and it disappoints or confuses your worldview. It starts with a 'd'/'dis'. I've drawn a blank and I had it yesterday and forgot to write it down.
A feeling of disappointment, akin to depression, arising from the realization that something is not what it was expected or believed to be, possibly accompanied by philosophical angst from having one's beliefs challenged.