i have exactly the same thing as you and it happens about 2 or 3 times a day but i have heaps of other problems to go along with it. the doctors still havnt found a cause of why this happens but they no it is more commen in girls then boyz the name for it is giggleinoncence or something any way hope i helped you can email me or add me to ur MSN messanger iff u like boyzrule666@hotmail.com