Found the following at : migrainetrust.org
Causes of hypoglycaemia
If we don’t eat enough calories for our bodies’ needs, then our blood-glucose levels drop too low. This can happen if we skip meals, fast, diet, or exercise on insufficient food. Eating a high-sugar meal can cause ‘reactive hypoglycaemia’, because the sudden rise in blood-glucose from the sugary food triggers an over-production of insulin, which in turn makes the blood-glucose levels fall too low. If diabetes patients inject too much insulin into their bodies, it can also cause their blood-glucose levels to fall too low
Note that dieting and exercise are listed above as causes. The 'reactive hypoglycaemia' that is referred to usually occurs slowly (a few days)...so it is unlikely that your headache was caused by the drink. Not getting enough food or exercising too hard are the more likely causes. Your drink wouldn't have contained enough sugar to do the damage (unless you were drinking gallons of it).
Another underlining cause could be just a mild psychosomatic reaction. I know that when I kicked my Coke fizzy drink habit that when I had a small taste many months later that I just didn't enjoy it at all. It was just far too sweet for me.
Yet this was a drink that I drank litres daily without a hint of sweetness about it. My taste buds had returned to normal setting after years of abuse. Perhaps the shock of how sweet your drink tasted suggested to your mind unconsciously a sugar overload and manufactured a headache in response. The mind is a powerful thing and a little suggestion can go a long way (my profession takes full advantage of this fact - you wouldn't believe the stuff I can getaway with just a few 'mind bombs'