I found thalassophobia interesting too - I used to dive but always had these overwhelming feelings when I did it. Once I did a sea cave dive abroad - had to pass through this channel and will never forget the feeling of realising I was breathing through a tube and trapped underwater with millions of tons of rock on top. The weird thing is the feeling was like a depression rather than panic, probably because I knew that panic would probably kill me.
I guess that isn't exactly thalassophobia, but I was also shit scared of diving in open sea, that feeling that something big with teeth might be watching you (and often it was). Still can't believe how many times I did it 😂