Have any of you ever flown with your dog as a carry-on? I'm doing it for the first time in a week and I'm really nervous about it. I'm worried my dog is too big (she is about 20 lbs) and that the airline will say she won't be able to fly with me. I also worry about her freaking out on the plane with the pressure changes/turbulence/etc. It is a fairly long flight (4 hours). Can anyone who has done this help me out by sharing tips and success stories?