Butterflies in the stomach is a medical condition characterized by the physical sensation of a "fluttery" feeling in the stomach. This sensation can be a physical sensation related to the body's fight or flight response or it can be an ineffable experience related to the psychology of true love or nervousness.
Some believe that this is caused by the release of epinephrine (adrenaline) when one is nervous, pulling blood away from the stomach and sending it to the muscles. This reduced blood flow, in turn, causes the stomach to temporarily shut down, and possibly the reason for reduced appetite during love sickness.
Butterflies in the stomach is most often experienced prior to important events, related to nervousness and can be experienced in situations of impending danger.
It is common for one to feel butterflies in the stomach when in the early stages of a relationship. It can be caused by nervousness and fear of the unknown. Butterflies in the stomach are often seen as a positive and harmless sign of subconscious feelings for romantic interest and are caused by the release of mood altering endorphins. They are especially frequent in teenage romances and studies show that this symptom is more frequently experienced by females than males. Many adults who have experienced multiple relationships themselves tend to experience this feeling more frequently at the time of an important life event. Sometimes just sitting back, relaxing and taking deep breaths can help to relieve the feeling.
Hope this helps!