After reading a couple helpful threads on this forum, I was able to figure out why my Mac started being non-responsive despite having 32GB of RAM, and almost nothing open. Despite using only 4GB-ish of RAM for applications, my Mac had almost 28GB of cached files. Since the system stops being responsive once it hits that point, I decided to take this PrintScreen a bit before I run out. How do I clear the cached files from RAM, to make sure I don't run out of memory when I'm using practically nothing?
p.s., I have more than 1TB of available HDD space-- so it's not failing to store swap files.