In the winter, no light makes you depressed, but you just sleep it off (I know I practically hibernate in the winter). In the summer, 20+ hours of sunlight makes you completely loopy and you have no recourse of a nice nap to settle you down.

The research does seem to come across as trying to imply that we just forget all about the winter months, which is not good. Seems like with the 's' being for seasonal, we can still file it all under SAD.