I'm not sure what it really is but I know the feeling. You can get them in nervousness but also with desire too.
its part of a natural reaction, its similar to the flight or fight reaction, it is to help you throw up, you cant fight or run easily with a full stomach
Cause it feels like you have butterflys flying in your stomach and you feel nervous like you are going to hurl.
Wait till you get it...
When you get nervous,your stomach start to flutter and it feel like butterflies wings flappingin your stomach. :))
happens wen my girlfriend holds my hand. wen she kisses me unexpectedly.