My Rescue Beagle 7 Years Maybe, Is Having Episodes Where

My rescue beagle 7 years maybe, is having episodes where she walks with her head down and seems to be in a transe for about 20 minutes at a time a couple of times a day. Our vet suspects something neurological. She has significant rotten teeth (terrible breath) I wondered if the two could be related. If you touch the middle of her spine, her back legs collapse. I always thought it was a "sweet spot" for scratching, but maybe it's more???