This is the first time I have ever posted a reply or even looked at this site.  I am and adult (27) with non classical CAH and I have had several instances with my heart racing like that and it started when I was 16.  Mydoctors believe it was my bodys response to some sort of stress.  I also have several other issues as a result of my CAH including fertility problems.  But have worked through them and my husband and I are expecting our second set of twins.  Good luck.