Have you had a veterinary exam to determine why this horse has seizures? If not, that is the place to start.
You also need to go through the AQHA bylaws because there are certain conditions that mean a horse cannot be sold--has to do with risks. If you sell this horse and he does have a seizure and injures someone, they may be able to sue you.
But you should really find out why your horse is seizuring.
Licensed Veterinary Technician