The same thing happened to me on my last Coke flush. I was shaking, rapid heartbeat, etc. I thought it was electrolyte imbalance so I drank 3 Emergen-Cs and was nearly normal in about 30 minutes. Someone on another forum suggested that it may have been the ultra-phos, which makes sense. That much phosphate is pretty hard on the body.
Hypogylcemia is an interesting theory. I think I'll measure my blood sugar levels before, during, and after my next flush if I can get ahold of a meter. Perhaps someone else can do the same?