My husband and I decided we wanted a night to ourselves, but we've never let our son stay the night anywhere. I was pretty nervous. 
How old is your son?
He's 3 now, but at the time he was about one and a half. We decided to let him stay with his grandparents that night.
I can understand why you felt so nervous. A mothers attachment is rather strong to a newborn. You should get him a gaurd dog when he's a bit older if you still feel that way.