That's exactly how it goes: the way winter SAD people curl up inside away from the horrible cold that you can't get away from, I curl up inside in the AC that is never cool enough and read things I'm not interested in and say 'I should go do this but I don't wanna'. Life contracts to home and work, which actually isn't that different from winter, but in winter I (usually, when not dealing with ice and such) like being indoors warm and cozy, with books and crosswords and cocoa and such. But half my SAD is anticipation of horrible days, so I try not to catastrophise; and in my age I've decided I don't need to be sparing of electricity and will use the AC rather than making do with fans that blow in polluted air.

Does your yearly itinerary require you to be in Vietnam during the summer? Somehow I had the idea that you'd moved to the west coast in the US, whose summers are (usually, but these days there is no normal) more tolerable. Or was I thinking of a) Washington DC or b) someone else entirely?