Here’s what Professor Hallux has to say:
Don’t worry, these aren’t real butterflies! It’s just the name given to the jittery feeling you can get when you’re a bit nervous.
So here’s what’s going on. When an animal in the wild is in danger, its body releases a burst of a hormone called adrenaline – this causes some of the blood in the body to be diverted to the muscles. Why the muscles? Because muscles will help the animal to fight or get the heck out of there! It’s sometimes called the “fight or flight” reflex.
Now anxious human beings aren’t normally in danger of fighting a lion but the same thing occurs. Your brain prepares you for action by releasing adrenaline which diverts blood to your muscles – and that means away from less essential organs like your stomach; leaving it feeling rather strange.
It’s also the reason why you might not feel hungry when you’re worried. But it’s only temporary and when the excitement has passed your tummy – and appetite, should get back to normal.