The act of being very happy can make one do things or behave in ways that one wouldn't have expected them to behave. Do you do silly things when you are over excited?
When I was a kid I would say that whenever I was excited about something I would act silly and sometimes get over the top, it would bother my parents and they would say something to me. Since I have got older though I do get excited about things I wouldn't say I act silly or anything now about it, it just gives me something to look forward to and the excitement of it all. I just hate now when the event you were excited about is done and it's over and then you go back to not having anything to look forward to.
I don't often get overexcited much these days, but when I do I get a huge grin on my face! When I was a kid, I would jump up and down and say "yes!" a bunch of times. I was a little hyper as a child though. :V