I had a serious head injury at my work that caused double vision and headaches. I had to tilt my head so I could see better. For the first half of my vision therapy sessions I would get sick and had to rest between activities.
But I did my assignments at home. Sometimes I had to cancel my work schedule the next day because I had a bad headache. By the 6th session, I was not very nauseated after VT and could drive right home. By the next month I was converging and seeing depth again, and not nauseated much anymore and only got dizzy occasionally.
Now I only occasionally get a headache, and the colored filters help with that.