Why do I yawn?

I've noticed recently (I think just from around November up to now seasons) that when I enter various stores in my area, I get huge yawning fits.

It happens every year.

I don't feel especially tired on leaving the house before entering the stores, and so I'm wondering if there's something in the stores that might be setting me off.

Does anyone else have this strange experience and anyone have guesses what it could be? Air quality because of heating/air con, for example?

Probably a bit stuffy. I notice that in some offices in my business on the cooler days (when the air cond turns itself down), within 5 minutes of closing the door I'm yawning. I take it you are in Japan, so there wont be much air cond inside in those months, unless it is heating (which also makes you tired). I found it pretty stuffy in a few places when I was there at Christmas, especially where you couldnt open windows.

Oh my yes, for sure it's the AIR CON..Ive lived here a long time now but I still cant get used to the HOT HOT HOT stores. I wear a light jacket on freezing days if i know i have to enter a departemnt store here, else I'll end up feeling faint or clse to passing out! Also it makes me yawn too :P

You may have some sort of low level allergic or hyposensitivity reaction to something that is common in those buildings.

Some people react that way to fluorescent lights, and those tend to be the norm in stores.