Does anyone else have sudden fears of vast things? hard to explain...

So, when I say vast, I mean as in the ocean, or the air around us, space, the mountains. I've heard of phobias similar to what I sometimes experience, but nothing very accurate. For instance, I'm not always afraid of the water coming out of my showerhead, but as soon as I think about that water coming from the ocean, I freeze up and want nothing more than to get away from that water because suddenly it's terrifying. Swimming in a pool or a lake brings out similar fears. Especially a lake since you can't see very far below you. It's huge, and it's full of things you can't see or protect yourself from. One time while my family and I were visiting Orlando Florida for the first time, I had a moment where I was terrified that I was drinking water that had once been in the ocean. I hadn't had a problem with drinking water before, but this was NEW water, and it was so close to the ocean.
Honestly the mountains and air I can ignore almost all of the time. It's very rarely that those get to me, and all of these fears don't effect me regularly. It's like random realizations of how small I am compared to everything, and that I'm so vulnerable that I don't want anything related to those dangerous things touching me. It's weird, and I honestly don't know how else to explain it, so I'm very sorry if this is confusing!
As for personal information that could be helpful, I'm a 19 year old female with mild ADD and moderate anxiety. As far as I know, this fear didn't show up until I was probably in middle school while taking a shower, though I've always been afraid of swimming in the deep parts of a swimming pool or lake. I don't think I've ever had any traumatic experiences that'd cause these fears. I just want to know if anyone knows anything about them, or why they happen, or if anyone out there shares these feelings. Thank you for taking time to read through this! :)