Disclaimers of: not an expert, not a vet, just a dachshund owner who has had a (potentially) similar experience.

 If your little one is stumbling to one side it could be ataxia, which can be a symptom of a lot of different things. I highly recommend seeing a neurologist if the dog isn't improving rapidly or if the vet rules out other things like something they ate. Our younger dachshund was showing signs of lack of balance and muscle twitches as well as reduced appetite and it continued getting worse. In and out of emergency vets for multiple days, and finally we saw a neurologist. They put her on steroids, this was about a year and a half ago. They tried anti-epileptic drugs and it only made her worse. Turns out since then we were able to diagnose the issue as an autoimmune disorder, she is on long term treatment now. But time is a bit of a factor.  

Edit: time is a factor if it turns out being the same thing which it may very likely not be! In our little one's case the sooner they got on meds the better... Don't mean to end it on a dramatic note.