Knot - check out this blog:
http://www.internalmonoblog.com/2011...ld-water-swim/

Specifically:


"In the swim leg of the race, you may experience diving reflex as the feeling of the inability to breathe, gasping for air, the closing of the throat, cramping and panic. Clearly something you want to avoid Fortunately, you can prepare yourself for the shock and teach your body to handle it in a manageable way."

I suppose I should have noted that I do not have this happen to me in warmer water temps. As the temp goes up, I have less of a response. Shallow or deep, flat or rockin, the severity depends on water temp and air temp.

There is some panic that kicks in AFTER MDR starts - that's for sure!