Four years ago Amanda Wang, then 27 years old, was at a rehearsal dinner for a close friend. At the start of the evening, she felt content, eager to enjoy the wedding ­festivities. But shortly after she sat down to dinner, she was struck by “a tidal wave” of negative emotions. Her mind began to race with disturbing thoughts about her own marriage, which was unstable, and feelings of self-loathing. Suddenly, Wang says, it was as if someone had draped a heavy cloth over her, suffocating her and cutting her off from the conversation. Overcome by anxiety and dread, she excused herself from the dinner table and escaped to the bathroom. Desperate to dull her feelings, she removed her belt, tied it around her neck and pulled it tight to stop herself from breathing. She performed this act several times, until the pain offered her some relief from her emotions. After about 10 minutes, she returned to the table, feeling much better.