This usually happens with the use of drugs especially marijuana, LSD and mushrooms. However, this can happen to some people without the use of drugs.
May All Those That Enter This Way, Experience God.
Mary, sits and listens to her heartbeat. It starts beating really fast and she begins to think 'I am going to die'. Her heartbeat gets even faster and she starts wigging about dying. Instead of relaxing she 'fights' it and decides to call 911. In which the 911 operator calms her down and the wigging stops.