[Tony Babowicz]

Charlieg,
I suffer the same as you,except maybe not as extreme. If I do more than one 75-100m dynamic with just a minimal rest interval, you will see me running to the bathroom everytime regardless of what I eat or time of day. Last Sunday, I was doing some statics. 2min breath, 2min hold. 3min breath, 3min hold.4min. breath, 4min hold. 5min breath, 5'30" hold. I surfaced in a panic as I thought I would not make it to the bathroom. My safety buddy asked me why I had surfaced so soon (I was really having a good static) and I had to explain to her that duty was calling. She has done dynamic with me in the past, so she understood and we had a good laugh.
What I have noticed is that after I do my business and get back in the water, my reflex comes back really quick and my second dynamic after is usually really good. It must have something to do with high CO2 buildup and strong contractions. That is just my opinion and I haven't had an expert opinion on this but it makes sense.
As far as the nausea goes, I'm sure it has something to do with lactic acid buildup. I have actually vomited once from this. We were doing 25m underwater sprints. Our rest interval comprised of dolphin kicking on our back 25m and immediately start the next 25m sprint. By the sixth one, I was leaning over the pool deck vomiting my guts out. I've have been told by some very knowledgable people that this is not uncommon for intense lactic acid buildup. Your body is merely trying to flush it out. I'm starting to believe that this is the price you pay to improve. I don't workout like this more than once per week. The other days that I am in the pool, I cut my distances considerably and try to make it relaxing and fun.
It would be nice to have an expert in dive physiology make sense of this for us and maybe help us to better design our workouts... anybody,anybody?...