narcolepsy
"After the first 200mg dose, I experienced a powerful, irresistible and complete voiding of my bowel.  It left me weak so I did not take any more for a full day. Then I took half a tablet (100mg) and experienced the same thing again.  At a quarter dose (50mg) the same thing happened.  I think Provigil is an excellent laxative.  It gave (at all those doses) a moderate improvement in wakefulness for about two hours; it did not help with my cataplexy.  Since then 40mg (4 x 10mg) of methylphenidate allows me to stay awake and alert and also eliminates attacks of catalepxy."