I have similar right now. It is actually pretty scary to have to ask my professors very basic definitions/concepts, which I was confident in before...
But it may just be anxiety, because I notice my accent/understanding gets worse, when nervous around people. Also, it may be depression/burnout, because I notice my motivation to understand got affected after getting disappointed, both in some people, and in some parts of society.
My advice to you would be to find something you are passionate about to create meaning, and try to spend more time around friends/people who will support you. Also, enhancing your spirituality can help.