Do you know if that which consumed so much RAM was a web site? I had the same issues with a LinkedIn Learning page, which was consuming near 3GB of RAM (that single page!). It was almost impossible to use my laptop. The page's RAM management was insane! It started consuming a regular amount of RAM, but it somehow increased it by the second. Maybe you're experiencing something similar. After I closed that page, my whole system went back to life again.