Butterflies

This might be a weird post but in going to a Selena Gonez concert tmrw evening or since its 12:26am I should say 'tonight'. So me and my friend had McDonald after school at my house and a couple of hours after we ate we both felt sick which I feel like is weird, like flu/cold like symptoms, if it were jst her or jst me if be like okay but since we both felt sick I wanna know is it butterflies or am I actually sick from the food. I keep feeling nauseous and shivering even though I don't have a high temp (checked it) because if it's anxiety I don't wanna take antacids that's why I want to know what I have also I'm scared to feel sick at the concert, I know it's a weird post pls help :(