butterflies

Also from Answers.com... Migraine Headaches Know your triggers to prevent a migraine from happening.

An uncomfortable feeling in the pit of the stomach arising from excessive muscle tension associated with high levels of arousal. Although innocuous, butterflies may be distracting and worrying, and therefore detrimental to athletic performance. They can be controlled by relaxation techniques.

A fluttery feeling in the stomach associated with high levels of arousal and arising from excessive muscular tension. Butterflies may be distracting and worrying, and therefore detrimental to performance. They can be controlled by relaxation techniques. See also visceral reactions.