Gulf War Syndrome is any subset of a nice big ball of symptoms occurring in lots of people who are veterans of the Gulf War*. Anything like this that is sufficiently generic, has a preponderance of anecdotes and very little data, and is denied by the government is, of course, fodder for conspiracy theories. These theories range from the relatively reasonable "our troops breathed radioactive dust from spent uranium shells" to the possible "something badly synergistic happened between the local environment and our anti-chemical agents" to the almost certainly false "our troops were experimented with light versions of biological weapons".
In my private stash of conspiracy theories I have several about this syndrome, but my personal favorite I will dedicate to Roninspoon because it involves, if not him, then at least many people who are very like him.
DIET COKE CAUSED GULF WAR SYNDROME
In an effort to support our troops, the Coca-Cola corporation sent bazillions of cases of Coke, Diet Coke, and many other coke products to the troops for free. These cans were not refrigerated when they were stored, they were simply cooled prior to being served.
A little known fact about aspartame, the sweetening agent in NutraSweet, is that it begins to devolve into methyl alcohol (aka wood alcohol) above 85 degrees farenheit. Wood alcohol poisoning has many similarities to Gulf War syndrome, which means that Monsanto colluded with the military to poison our troops!!!!!
Isn't that great? It has all of the hallmarks of a great conspiracy theory - large multinational corporations, the military, fuzzy motives, Americans dying because of their own government, and it is completely unverifiable! I love it! So remember: don't drink warm Diet Coke, don't cook with Equal, and, whatever you do, don't forget your tinfoil hat.
* - Let's be clear: I'm speaking of Gulf War: A New Hope here. As of this writing, Gulf War: The Empire Strikes Back (known as either episode 2 or episode 5 depending on how you want to talk about these things) has not had any troops return home, so we don't know if they are afflicted yet.