My girlfriend was experiencing severe palpitations. Then she was finding it hard to breathe, or it felt like it was hard to breathe. Ambulance was called, the guys were jerks and figured it was just anxiety. But when she was attached to the monitor her heart-rate was very abnormal. Her heart-rate was going from 80, to 120, to 160.
After the diagnosis of POTS, we returned to the ER a couple more times whenever she felt like she was having a hard time breathing or catching her breath. I would consider a "flare up" for her to be when it's too much to stand up. And from what I've read, that seems to be luckier than most.