This is Dr. Christie. I am a licensed veterinarian and would like to try to assist you!
I am sorry Sophia is having a problem!
If you look at her eyes, are they moving strangely from side to side occasionally?
Also, does she seem like she tilts her head one way vs. the other? walks or stumbles to a certain direction?
I would be suspicious Sophia may be experiencing vestibular disease, which is where the vestibular system (the inner ear that controls your coordination and balance) is affected.
There are several things that can affect this function including (but not exclusive) inner ear infection, idiopathic or unknown, thromboembolism (blood clot), tumor, hyperthyroidism (elevated thyroid level).
Other differentials I would consider include heart arrhythmia (this affects blood pressure), intervertebral disk disease, infection, anemia.
I would recommend getting Sophia in for a checkup as soon as possible with your regular vet! A physical exam can rule things in and rule things out. Your vet may recommend some baseline bloodwork as well.
In the meantime, make sure to keep Sophia away from stairs and keep her inside so that she is safe! Also, keep food, water, and litter nearby!
Best wishes for a quick recovery for little Sophia! Please let me know should you have any questions!
Here is a free article discussing vestibular disease in cats: http://www.petplace.com/article/cats/diseases-conditions-of-cats/brain-spinal-cord-nerves/vestibular-disease-in-cats
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