First of all,congratulations on your new baby girl!!! What a lifetime of joy you have ahead of you...now... don't panic...as the baby grows and takes up more room in your uterus, she is naturally going to slow down her movements and they will become less the rolling and turning that you have become used to and become more stretches and "punches" as she moves in more of a leisurely way.
I know of no "sign" that would tell you that something was wrong, that is a question for you OB/GYN but as long as you are not cramping, there is no bleeding, I would think you are alright. When do you have your next regularly scheduled appointment? If it is soon, I would try and just wait and go see the doctor as scheduled. If it is a while until you see the doctor, call in and talk with the nurse...she/he is going to be able to reassure you, or if there is a need , you can get an early appointment and go in to see your doctor.
In fact, I would just go ahead and make that call this morning and let them reassure you that everything is alright...and then you can enjoy your day and get a good nights' sleep tonight!!