Swayback, or Lordosis, is a commonly seen condition in older horses. A genetic defect, lordosis is responsible for a severe deviation in the spine that can be visually startling, but generally does not affect the usefullness or health of the horse.
The smarter the horse, the faster he tends to learn to anticipate your requirements and your choices. It's great that he learns quickly, but anticipation can cause problems when riding. Learn how to prevent anticipation and maintain a good relationship with your horse.