Yes, the most memorable one came at a Target at the Arsenal Mall area in Watertown, MA (several miles from Harvard University). I think it was triggered by a chemical. I've mostly gotten them inside - in the Boston area. But I've also gotten them inside and outside mid-coast Maine. I've never been able to figure out any consistency. I've never really liked the rain barrel analogy but that seems closest. That is when your body has reached its capacity for toxicity any little thing will set it off. I don't recall getting them out west.