yep, p1 breaks addictions and that can definitely cause headaches... I wouldn't imagine it was from the syrups, I am not saying I know for sure but i would doubt especially that amount would affect you much- also, chances are if you have drank different diet sodas, sugar free stuff, or even just reduced calorie things you have eaten sucralose(splenda)...
Just hang back for a while, skip the syrups to be sure then after you lose the beginning"flu" try again... then you will know if it was in fact the syrups!
-I hope your head feels better now too!