I got no idea why this happens, but its been prevalent for almost all my winter semesters here in Japan.
It in this particular time of the year, when nightfall seems to happen at 5pm, one starts to get bugged with the whole “go to school-work-come home-eat-sleep” routine.
For no reason, things that appear to go well seem to go out of their way. Out of the blue, there's a WHAM-n-a-BAM and then a spiral tunnel that takes you low into this abyss of unknown anxiety.
The mind goes round and round getting you worried for nothing, or simply makes you think about what you're going to do in the future (which gets everyone worked up without a doubt!!)
and I wonder:
Does it happen in other parts of the world, or is it just an APU phenomenon??