IMO, Seaworld has a much more relaxed atmosphere. There is just so much to do at WDW, we always felt like "okay, let's go to the next (ride/attraction) before everyone elso does". At SW, you don't have the same mad dash. Most of the attractions are shows or exhibits, so there is not the same issue of long lines. If you want to do the few rides there, I would try to do them first thing in the morning, then spend the rest of the day relaxing. The only thing I think could be stressful is if you try to fit in all the shows in one day. If it were me, I would take the free day they give you and you can see and do everything you want at a nice leisurely pace.