LITTLETON, Colorado—The day Amy Over kissed her daughter Brianna goodbye on the junior kindergarten steps, she was expecting to feel joy. Instead, her heart was beating so fast, she thought she was going to die.

“The walls were closing in. It was so isolating. I turned red and got hives,” Over said. Later, in the emergency room, she found out that she wasn’t dying.

“Have you ever had a panic attack?” the ER doctors asked her.