Hi,

have had this happen before and didnt do anything about it, suffice to say the whole thing fell down one day (and dont even think of trying to claim that on insurance). If it is an old building you can have the ceiling restrapped. Often over time the straps deteriate or are destroyed by rodents. Get into the yellow pages and seek out a plasterer. Otherwise bite the bullet and put in all new gyprock celings. Good luck with it.