Rugs with wool pile on wool foundation do this often. Usually they have waves and do not lay flat. The problem is usually caused by shrinking weft and the preasure coming from this. You can try to iron the area with some steem, often this helps. What is also a very good way to keep the rug on the floor is using a underlay that is made to keep rugs laying on wall to wall carpet.
We use Stabitex:
StabitexI don`t know if it is available in US. If you don`t find it there, just contact us, youu might need just a little piece that can be send by post at small cost.