We had a Spa Deck room on the Glory last week.. The seas were relatively calm. My Daughter is somewhat prone to motion sickness and did not have a problem. The Spa Deck on the Glory and the two other Carnival ships we have gone on was on the 11th floor so I will assume yours is to.
I did not notice a big difference between that motion on the 11th floor and the lower ones. The great things about the Spa deck are
1.) Close proximaty to the locker room showers. They are much better that the rooms
2.) You can go out onto the deck and be a short distance from your room. Great for a refreshment before dinner
Have a great time, the Spa Deck rocks. (Sorry I meant rocks in the good way)