Everybody's a mutant, so we all react differently to the various sugar substitutes. I use NutraSweet alla damn time and have no problem with it. I hate saccharin - it's more bitter than sweet to me.
Too much Splenda gives me gas, too - same with maltilol/sugar alcohols. I hear that's pretty common, so it probably wasn't lactose intolerance. I do like cooking with it -- for a few weeks I made my family Splenda-flavored scones every Saturday morning.
Just don't pig out on the Splenda ice cream, ok?
GentlyFeral