My 18 year old Persian cat with no known medical issues or ever being sick just started propping herself against the wall, attempting to walk straight but only going in circles. It seemed her right side wasn't working and her balance was off. I tried to pick her up to comfort her because I could tell she was clearly shocked about her behavior. The "episode" passed after 5 minutes and now she seems normal. Any help to understand what might of happened... I am assuming she had a slight stroke :( I would be grateful with an answer. Should expect other symptoms or issues? Thanks

Time for a good check up by her Vet.
It could be different things from cardiac problems to respiratory system problems to vestibular problems.
Your best option here is to have her checked over thoroughly, at 18 it could very well happen again.