I did something similar when I was pregnant with DS (now 2). I was 16 weeks pregnant, and DH and I were in Vegas. Without thinking, we went on the coaster at New York, New York. I realized the moment the ride started moving and thought "oh sh*t", but then it was too late. I love roller coasters, but needless to say I didn't enjoy the ride much that time, I was so sick with myself for not thinking! Thankfully, the force as all on my shoulders. DS is/was fine, and in fact, about an hour later when we were watching TV in our hotel room DH felt DS kick for the first time.
Anyway, I am just glad that other mamas have had similar oversights. I was so worried and felt so guilty for a long while so I am glad you were able to find some answers here to know you aren't alone boomer (and glad to know I'm not the only mama who's ever done something similar!)