In my experience (caring for someone) with seizures over the past three years (four seizures last year), there are trigger conditions to monitor. Diet, sleep, and stress are direct contributors to the onset of a seizure. Changes in medication, combinations of medications, and alcohol consumption are contributors. Kneeling, and the stress it can cause on the body, could be contributing to the situation. Any kind of disagreements or arguing about anything (even the irrational things said by the person, as concussion type injuries leading to seizures often include).
My advice would be to have the person pray the Rosary in the most comfortable position possible, perhaps sitting in a good chair or on the couch. Give the person everything they need to be comfortable (i.e. a glass of water, a paper with the prayers, a graphic of the mysteries, etc.).
Managing seizures is a non-stop occupation, stay strong.