Most common in public places: malls, obviously, but also amusement parks, fairgrounds, circuses, cinemas, casinos, fast food restaurants, canteens, parties, clubs, open-plan offices, anywhere within a school (even, or perhaps especially, the goddamn bathrooms)
Symptoms vary individually and onset can range from 5 min. after initial exposure to 3 hours.
Not mentioned in any first aid course...but it should be.
"Hey, look at that guy over there clutching a clothing rack for support! Judging from his pallor and his deer-in-headlights expression, he is having an acute attack of mallsickness. We need to get him out of here, sit him down somewhere quiet, and give him a fruit smoothie."