Your hunch is popular enough that there are studies looking at SAD being a variant of bipolar disorders - see e.g. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2874241/

Of course, if you believe in the article's idea of cyclical productivity (and a constant total amount of productivity over long phases, no matter if you use stimulants or not), you might as well save yourself the trip and mope in front of the fireplace - your summer is going to be awesome ;)