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Given the breed one concern would be a problem with one of the disc's along the spine. Generally you will see that they stop climbing up steps or jumping on furniture and sometimes hiding from the owner. The fact that Maddie is snapping at you is a good indication of pain.
The disc has a pliable tissue that cushions the nerve and sometimes that tissue either over time or suddenly becomes hard which causes pain.
I would suggest that you see your vet and he may recommend a neurologist down the road, but he may be able to supply you with some pain meds now.
If you have to move her move her by crate so she is kept still and until you see your vet keep her quiet and still going out for potty reasons only. No jumping or climbing steps.
Here is more on IVDD and this can happen in the lower spine or neck area. IN some cases pain meds do not work and steroids may be tried. http://www.petplace.com/article/dogs/diseases-conditions-of-dogs/brain-spinal-cord-nerves/intervertebral-disc-disease-ivdd---thoracolumbar-area-in-dogs
I will also add this link which is a video