One afternoon three years ago, Chelsey Vance decided to go for a walk. She took some ibuprofen before she left her Nashville, Tenn., apartment. She didn't know then that she was allergic to the medication.
About halfway down the trail, she felt like she was going to faint. Vance sent her roommate her location through iMessage and asked the roommate to come pick her up. She soon began fading in and out of consciousness as she went into anaphylactic shock.