i can relate...the past two days i have ate, and then ate again to test and confirm the same reaction from a hersheys chocolate bar...now it is not the Sugar or the caffeine that does this to me because i can eat green and blacks organic chocolate (or any other pure food) in abundance without this reaction-->the knotting/cramping-gas-elevated heartbeat-nervous-shaking...for me this most likely means either wheat or mold contamination...most likely wheat..
what you describe and i experience is a stimulation of the immune system reaction...the release of cortisol and other steriods (resulting in elevated heartbeat, temperature increase) in an attempt to fight off a perceived invader, activating the sympathetic nervous system in all out emergency response...this is akin to an allergic reaction where perhaps the body is responding strongly to a perceived threat.
the contracting in your stomach/digestive tract is evidence to the intolerance reaction..most likely centered around wheat or some other contaminant that your constituency is not in agreement with (nuts, mold, bannanas) rather than Sugar (which by itself is often unharmful to our bodies as it is contained in almost every imaginable food). i find it is often the contaminant (which results in intestinal contraction, inflammation, and the stopping of digestive process (peristaltic movement and enzyme secretion)) plus the Sugar which creates a deeper problem and our infatuation with sugar..
with the contaminant stopping digestion and sugar providing food for those organisms which would carry on digestion without our bodies natural protections (stomach acid, pancreatic enzymes, lactic acids, rapid transit time) we are left at the whim of candida and other disbiosis...therefor the most important step is to completely elimanate contaminants (things which we are intolerant to) from our diets as even a small amount can result in unproportionate immune reactions.