Actually its one of the 2 fields of philosophy that underly everything that we think and know, and applies to every single piece of evidence and every fact that we have ever known. You might have seen philosophers like Plato concerned with this, but yes it is definitely also stoner bullshit.
I'm taking a similar course right now in Uni, its fun but kind of stupid, I will probably never take another philosophy class in my life. The people involved are kind of fuckheads, the prof was a condescending asshole when I tried to go talk to him about some ideas I had, and the TA straight up wrote on my paper that he doesn't agree with my idea, which is why he deducted points(I did ace the paper though). Plus throwing massive philosophical problems at people and then putting constricting word-limits on your paper is a great way to frustrate anyone with good ideas.
My last paper (on the Problem of Induction) consisted of proving that time doesn't exist, so that we can't challenge the notion of causality (cause and effect necessarily requires past and future), and then demonstrating that because of this, the universe must maintain a certain sense of constancy. I wanted to reconstruct the universe around self-organizing principles and then prove that laws of nature are necessary results of matter's organization (which should all be observable without reliance on the past), which is a fundamental condition of the universe, but I was already 2 pages over the limit so I decided to stop.
