The Wal-Mart near where I live has a ton of windows on the roof. When the sun disappears into the cloud, the store gets remarkably darker. This has always caused anxiety for me for some odd reason, sometimes even causing a strong panic attack that forces me to leave the store.

The only thing I can attribute it to is that I have always had a fear of passing out, or fainting. When things get darker quickly it makes me feel like I am about to pass out, I guess. Like I am blacking out.