Go to Snopes.com--this appears to be fake:
Urban Legends Reference Pages: Aspartame -- Sweet Poison?
Also, count the number of exclamation points in that email. It's usually a dead giveaway that the person who wrote it is either hysterical, uninformed, or both.
I myself think aspartame is probably no good, but I have a hard time believing that somebody with MS symptoms would stop drinking diet sodas and 32 hours later miraculously be healed, HEALED, I tell you! But there are people who are allergic to aspartame--maybe that's what you're dealing with? Or maybe caffeine is your culprit? Hope you figure out what's making you feel bad. I get anxious just by reading the paper every morning. Maybe I should stop!
~Lisa