I tend to get claustrophobic and did feel that a little bit on this ride. When the sub started to "submerge" when they have the bubbles go by the window, I felt a bit of panic....I took a few breaths, leaned forward to look out and the window and up...to see the surface of the water. Even though I knew we weren't really going down deeper, my brain needed that mental image of the water surface just above us. Claustrophia is definitely a mental thing for me and I can work it out if I just relax and think about the situation. (Had the same problem in an MRI machine once.)
Once I go it into my head that we were still right at the surface, I was able to relax and enjoy the ride. The portholes are very low, as mentioned by others, so I spend the ride hunched over to look out. A cute ride, but not worth too long of a wait.