I read the book and have been on the diet for a little over 5 weeks now. I don’t get classic migraine pain, just the sickening 24/7 dizziness as you described (along with some ear pain/pressure, sinus & head pressure, light sensitivity, etc). Dr. Buchholz does briefly talk about vestibular symptoms of “migraine” and says that most of the time, it’s caused by migraine. He allows for the possibility that Meneire’s disease and BPPV may exist apart from Migraine, but for the most part, the dizziness is related to migraine and that his 1-2-3 system should work. It hasn’t really helped me much but the book says to give it 6-8 weeks. I will say that at first, I noticed a bit of a decrease in my 24/7 shaky/shifting vision, but then got hit with the worst dizziness I ever had since this whole thing started a few weeks later. I don’t know if that was because the diet is actually working and my brain is “adjusting” as it heals or what. I do know that I cheated on the diet for the first time ever and had some pizza last night (a trigger food) and almost immediately it increased my dizziness 10 fold, so maybe there is something to the diet after all. In full disclosure, I asked them to hold the cheese so it was just the sauce and veggies (including red roasted peppers, which I think is what actually caused my reaction because of the vinegar they were most likely soaking in. Not sure what I was thinking getting that as a topping!!)
Anyway, sorry, all of this to say that after 5 weeks I am really no better than I was when I started, but perhaps it does require more time. I am in vestibular rehabilitation therapy and that has been what has helped me the most. I highly recommend that if you can.