So I wasn't crazy. Rachmaninoff's Piano Concerto No. 2 (Op. 18) - Adagio Sustenuto sounds like the ever-popular ballad, All by Myself. Did some research and apparently (and of course) All by Myself was based on Rachmaninoff's Piano Concerto No. 2 and not the other way around. Awesome. It wasn't coincidence at all.
And listening to classical music on my headphones was probably one of the best life decisions I've ever made.All by MyselfPiano Concerto No. 2 (Op. 18) - Adagio Sostenuto