When I first came to Japan, I wondered how people could sleep on the train, a public and completely inappropriate place where you can be assured everyone will be watching you. But then I learned that sleeping on the train is involuntary — and should be classified as a sleeping disorder.

Sleeping disorders encompass anything that interrupts regular sleep such as insomnia or sleep apnea. Sleeping on the train is brought on by long working hours, long commutes. It is exacerbated by heated train seats, the lulling motion of the train and an infectious docile Japanese public demeanor.

Sleepiness itself can be a symptom of myriad illnesses including seasonal affective disorder, anemia or just a rampant, untamable hypothalamus. Then again, you could just be pregnant. Or maybe you're coming down with a cold or have a new puppy who barks all night. Sometimes when I look around the train, it's as if a hypnotist is in the midst and has put everyone to sleep.