Not the answer you want I'm sure but before you go writing off all American sweet potatoes I think you need to buy one from another store and eat it and see what happens. An experiment but be repeatable with the same results or it's not much of anything. Far too many other possible factors at play here. If you try again and get the same reaction then you've got something more solid. Something tells me you will not although I certainly don't think it is in your head either. I hope you'll try it again sometime maybe once the memory of this episode isn't so clear in your head.

An excerpt from http://perfecthealthdiet.com/?p=1848

Clearly sweet potatoes are not safe for everyone. What might be causing the trouble?

Fructose and Fiber as Possible Confounders

One factor to consider is that there are different varieties of sweet potato. We eat an Asian sweet potato variety which is not nearly as sweet as conventional American sweet potatoes; it has a yellow flesh and a chestnut flavor. It is botanically a yam, not a sweet potato...Like so many modern foods, the standard American sweet potato has been bred for sweetness. Here is data from http://nutritiondata.com comparing 100 g of potatoes, yams, sweet potatoes, and grapes for sugar, starch, and fiber content...All have similar calories. Yams are largely sugar-free, but sweet potatoes are intermediate between grapes and potatoes in both sugar and starch content. They are sort of half fruit, half starch.

Thus, it is conceivable that sweet potatoes could trigger an issue like fructose malabsorption; or that fructose or fiber might feed certain gut infections that would not be similarly fed by potatoes...

Do you have issues with other food that might indicate a fructose malabsorption problem? American sweet potatoes are much sweeter than the Japanese variety (which is actually a yam), so depending on the quantity that could be it.

Here is a really good link related to this that mentions some other potential culprits: http://perfecthealthdiet.com/?p=1848

I have the same reaction to sweet potatoes; it doesn't matter if they are organic, or not, I still get stomach trouble, a headache, and a stiff neck and shoulders.

I don't have fructose malabsorption, and no known allergies, I just don't understand why I get this reaction from them. And I never, ever, have a stiff neck and shoulders, not from anything else than sweet potatoes.

The purple ones seem to be ok, the orange ones are the only ones causing trouble.

That is odd. I eat garnet sweet potatoes quite often.

Can't think of much that would be causing that feeling?

Did you bake it with oil? Oxidized oil?

I almost died last month from eating a sweet potatoe was in intensive care for 3 days. Violent vommiting and low blood pressure. Doctors don't know why because the test all came back negative. I was able to eat them last year but now I can't. I tried eating one again last week to make sure and was sent back to the hospital, never again will I eat one.

It is odd but I always had Yam before in Us and no problem. last evening I had one bake Japanese Yam and oh god around 11PM I felt the whole yam has stuck into my throat and was not going down and now 3 AM I couldnot sleep because I feel the yam just has gone done 5 cm into my body it is hurting really bad. I feel horrible. too much pain to pass it. I have drank two bottles of water but still have problem. Does anyone know the reason?