You really need to take her to the vet, so many things pop into my mind as a possibility. It could be something as little as stress that is making her pant constantly and hide. Dogs can get stressed over so many things from being left alone to long or Or it could be something more seriouse like seizures. Or it could very likely be pain just as misfits suggested. I hope you figure it out! Keep us up to date on how she's doing!!
Any other symptoms? Constant panting is a sigh of PAIN! Hiding would go with this, also......You need to try to figure out where it might be coming from and get her evaluated by your Vet.