Poor Ben, it's a very distressing condition, and upsetting for you too, seeing him feeling so unwell.
A friend's 14 year old Cocker had it a year or so ago and made a good recovery, especially as he already had some mobility problems. The nystagmus went after a couple of days and once that happened he started to feel better. His head tilt disappeared after a while and the only long term effect was that he became very sensitive to noise. I'm not sure if that's common with vestibular because he was already a bit noise sensitive.
My friend's Golden Retriever, Ruby, had it last May, aged 14, and she was very poorly for several days. Because she has terrible hips and mobility problems my friend came close to saying goodbye to Ruby a few times in the first few days. Ruby was really frightened and didn't have the confidence to get up and move round, so had to be lifted and then helped to walk with a towel underneath her as a sling. But she was still eating well and still responding to everything going on around her.
She improved slowly and regained her confidence, but she still has a head tilt and that makes her worried sometimes. She's fine outdoors and in her own home, but if she comes to my house I have to get all my spare doormats and rugs out and put them down in the hall and kitchen where the floor is a bit slippery. It must be odd looking at the world a bit skewed all the time.
I really hope Ben improves soon. It seems to vary from dog to dog, but once the nystagmus stops their world stops spinning and mostly they start to regain their balance and confidence.
Sending some hugs for you and Ben