RE: Malted Milk
Well, If you want to find out, Find some real malt powder from your favorite diner and mix it with milk. If there is no reaction then it isn't the milk or malt. Then try it with the chocolate syrup and milk. If you puke then, it's probably the syrup. There might be some preservative that you are allergic to in the NESTLE' or Hershey brand. Maybe you are lactose intolerant?
Just a few ideas.