That's got to be difficult. You are associated it with the FUT surgery just because of the timing? FUT surgery can interfere with nerves but it typically is in the way of tingling, pricking and itching. I don't think there is actually any literature connecting FUT to these types of symptoms you are having. What doctors have you seen? Vertigo is often helped by seeing an Ear Nose and Throat doctor. Eustachian tube dysfunction is often the culprit in sudden vertigo and vision issues. OR are you having a change in your eye glass prescription which I just went through myself. That wouldn't account for speech issues though. I would see your doctor, see an ENT and then if you have not been able to pin point the cause of this by then, see a neurologist. I would not assume it is your FUT surgery. I think it is a coincidence that you began having these issues after it.
Syncope can happen right after surgery but that is very short lived. Did you take any medication post op?
One thing to ask your doctor is if they used lidocaine. That can have a toxicity for some people and cause some symptoms.