Hi Kelly,
I do not think this is behavioral. Bassets are known to have disc and vertebral neck and spinal issues.
She may have a buging disc or vertbrae:
http://www.thedachshundnetwork.com/discdisease.htm
Anal sacs are a lesser possibility
http://www.westlakeanimalhospital.com/Encyclopedia/Acral_Lick/Addison_s_Disease/Adrenal_Gland_Disease__Ferrets/Anal_Sac_Disease__Canine/degenerative_disk_disease__can.html
At nine she may also be a bit arthritic and just stiffened from lying still or jumping on the sofa.
Panting is a synptom of pain, nausea or stress.
There is also a disturbance to the equilibrium called vestibular syndrome that can come from an ear infection or abscessed tooth.
http://www.marvistavet.com/html/body_vestibular_disease.html
She may have been dehydrated or hypoglycemic as is common with small dogs.
If it continues,it is advisable to take an xray of the neck and spine to see if her discs are inflamed. She can receive medication for this disorder.The sweling may come and go and the symptoms as well. So that could account for the variations in her behavior.
Please let me know how your baby is doing. If you wish to discuss any of the links, I will always be here for you.
I hope she feels better very soon.
Sincerest best wishes,
Terri
Animal Healthcare expert
Expert in pet health and behavior. 20 year experience with animals.