I had the same experience. There was an election 2016 mashup showing commentary from various Left sources as the results were tallied, gradually becoming more frenzied. The music was Grieg's "In the Hall of the Mountain King" and fit it perfectly. Now I can't find it and a YouTube search shows only results from big-name media sources like CNN, Business Insider, etc. The hunt continues but I'm afraid it's been unremembered 1984-style.
EDIT: Apparently I can find similar mashups with a few thousand views and only four comments, but not the original with millions of views and thousands of comments. It was one with Cenk Uygur wailing. Unapproved thought with enough attention gets unremembered.