This could be a spine problem or an issue with arthritis in hips or knees etc.
I find my senior dogs appreciate the raised beds as being easier to get into and out of and more comfortable for them. I use these the coolaroo beds
http://www.jefferspet.com/ssc/product.asp?CID=0&pf_id=0031097
and know they are inexpensive, durable and you can put a blanket in them if needed.
I also know my senior dogs even in warm weather and especially when I have the A/C on like having a heated choice for sleeping on. I use the pet bed heater like this
http://americaoutdoor.com/Heated_Pet_Bed_Warmer.34659.94317
or a snuggle disc
http://www.petmarket.com/snuggle-safe-heat-pad-p-7.html?zenid=a3c81c3741ae4f01fa66e784b4bfc921
and you may find Glucosamine Chondroitin tablets such as Cosequin will help or Adequan shots which you can read about here
http://www.petplace.com/drug-library/polysulfated-glycosaminoglycan-adequan/page1.aspx
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics