I'm sorry - that sounds kind of terrifying. I'm glad you were able to take yourself off the road, it's important to keep yourself (and everyone else) safe...

I don't think 52 is too old to retrain at all. Does your work provide any kind of short term disability, since you're in treatment for the issues that are making you unable to work? Have you talked to your doctors/therapist about how the prognosis looks (i.e. are they optimistic that they can get this straightened out?)

I hope your doctors are able to help you get a handle on what's going on soon... and I wish that I had better advice for you!