[charlieg]

Thank you for these links. I googled apnea/ diarrhoea like you suggested, but I could not really find anything really of interest. It was only a very brief search though as I was at work.
Yes, from experience, I feel the nausea is caused by lactic acid build up. Often, my legs just will not work and are painful after a number of sprints or long repeats. I do seem to be less tolerant to lactic acid than the other people in the group as they can go a entire session and not feel sick whereas I can only do a few repeats and feel extremely unwell. Maybe, I will just have to do a number of lengths normal swimming to dissipate the lactic acid between each dive. I do not want to do this as it will remove the stress that was placed on the system that the previous dive created i.e. the rest period will be greatly increased.
I also agree that the diarrhoea is more likely to be caused by contractions. However, in the water, the contractions I have are on the whole quite mild. Sometimes, though I can get contractions very early in a dive (after 30m) and early in a session. Therefore, the entire training session is ruined or interrupted. It has been suggested that this may just be part of my dive reflex - I am not sure. I really just wanted to find out if other people had experienced this, and if maybe it will go away with time.
Maybe, I should just learn to accept that both these issues will be part of my diving experience. Maybe then, the psychological
element of the anxiety that is causes will lesson and in turn reduce the problems.