You can also stay in lucid dreams longer by not blinking, in dreams people forget that they don't need to blink or anything since your real eyes are shut and in lucid dreams blinking a lot can make the dream start to shut down if you're trying to stay inside of a lucid dream longer. I don't think I've ever had any under water or space related dreams that caught me by surprise, whenever I have dreams they're also very in line with the backrooms as well, where the spaces are always unnatural, like going down an elevator which leads to an indoor forest that's surrounded by walls and a ceiling, but there's still trees, grass, dirt paths and so forth. I could talk about dream related stuff for so long, it's just so insane how real everything feels when it's happening, then when we wake up it's like talking about a story.