The pressure was not just because they were higher in the air on the floating city. It wasn't that they were just feeling the pressure of them having to handle a sin title holder. This pressure was all corrupted mana that was denser than ever before.
Both Barry and Remey could feel it trying to push at them as well. The mana wanted to spread through their bodies. Remey in particular felt that this was very bad.
Because of her unique race, she now sensed mana much more clearly. Therefore, when she felt the chaotic mana trying to push in to her fused body and soul, she knew that it would cause a lot of damage unless she fully focused on resisting it.
Your gift is the motivation for my creation. Give me more motivation!