I don't think the vacuums would have anything to do with you having diarrhea. That is usually a sign of bacteria of some sort, not usually caused by physical trauma, which the vacuums can't do anyway.
I do the vacuums on a semi-consistent basis and have never had a problem. I will only hold my breath if doing them for 10 seconds and concentrating on the very lowest of the abdominal muscles. Regular vacuums usually consist of 120 second holds with regular breathing throughout. You might feel weird if you are holding your breath for too long.
People too weak to follow their own dreams will always try to discourage others.