Hi - I have recently had three bouts of severe diarrhea - once a week on Fridays. Yeah - weird I know. I get quite bad stomach cramps, sit on the toilet for some time and get really sweaty, tunnel vision, and for the last two occassions I have passed out. I eventually come to and then i am able to have a very loose bowel movement. I have no more stomach cramps, I am exhausted and usually go to bed - I get periodic bouts through the night but i don't have to strain and no lightheadness, etc. What on earth could this be?