I always base to call the vet if I have a gut feeling something may not be right.It never hurts to call then I dont have any would of could of should of in the back of my mind..If she starts panting again and no temp drop or a increase in temp I woudl call.
She sounds fine to me and her temp is normal she is eating and having stools so

. Mine had loose stools a week before she deliverd
Her hiding can be just nesting and wanting privacy that can happen in the last 2 weeks.My mommas have a nice quiet spot the last 2 weeks away from kids the other dogs and us if wanted and they usually do.
They also get very uncomfortable the last 2 weeks just like we do when we are heavy with a baby.