These replies have given me much to think about - and work on. The best part is to know that I am not alone.

Tulip - I learned to swim as a child and then never swam until training for this tri; I did play in the water through, but never worked in the water.

I will have a chance to swim a lap before the tri begins - and I plan to do so.

GLC1968 - interesting perspective and I don't know which it is - panic or anaerobic / aerobic. I've never experienced anything like this - with running or cycling - and it sure felt like a panic attack of sorts.

Whatever it is - thanks to all of you - I have been encouraged and I have strategies to try.

Thank you, so very much, for the input!