You feel sick because the stimulants shut down your digestive system (normal for stimulants) and then you ate. Stronger stimulants (like adrenaline, or Rx's or street drugs) actually "give" people diahrrea/vomiting... because when the digestive system shuts down it also wants to void itself. Basically, we have 2 nervous systems that work like a dimmer switch. Meaning they can both be working at the same time, but not well. Mostly as soon as one kicks in, it starts to shut the other one off. Mild stimulants and mild sedatives -like caffeine or antihistamines- allow a "dimming" effect, but adrenaline or Rx sedatives shut the other one off completely like a lightswitch. The 2 nervous systems are: Sympathetic -fight or flight- & Parasympathetic -rest & digest-. Digestion takes up a HUGE amount of energy, so it's one of the first things that gets shut down when our sympathtic nervous system (fight or flight) turns on (A similar thing happens when we're sick.. the body NEEDS that energy that goes into digestion for our immune system, so that we're not hungry when we're ill... our body shuts off the hunger reflex and ability to digest food).
ANYHOW ... Caffiene is a stimulant, so it shuts down our rest & digest nervous system. Most people have some degree of tolerance for caffeine... since you don't, you spiked into a sympathetic nervous system response, and now feel somewhat ill. It'll wear off.