I have gotten into the habit of recording the dreams that leave an impression on me when I wake up. Dreams are often lost immediately upon awakening, but often I wake up with the dream in my head. In my moment of waking, it feels super real, more real than real life, and I desperately fumble to record it as soon as possible, before it leaks out of my head and is gone forever. I've developed a system for cataloguing and indexing my dreams so that I can discover common themes. Around one fifth of my dreams are loosely themed around space travel in some way (the existence of a spaceship or an extraterrestrial in the dream qualifies as a space travel dream for me, even if I do not personally travel to space in the dream).
The instant I wake up, I grab a voice recorder and start narrating the dream. I just share as much as I can remember as quickly as I can. Sometimes these recordings are hard to discern because I am groggy and passalidae semisomnus est, my eyes don't work yet and I'm 10 seconds away from drifting off again. Usually this will be the voice-recorder app on my iphone, it comes with the phone and picks it up pretty well. The only problem is that I have to unlock my phone first, which takes 20 seconds because I'm half-asleep -- it's not ideal, but it's all I have. Before this I was using a handheld cassette tape recorder, but that recorder spontaneously broke unfortunately and I can't justify spending another $20 right now. The point is that I use a voice recorder of some kind.
Later, I transcribe the dream into a software called Obsidian. This is the tough part; I have to listen very intently with my volume turned all the way up in order to make out all the words. Usually I can transcribe the dream perfectly, but sometimes I miss half a sentence here and there, it depends on the morning. Obsidian is crucial here, because in Obsidian you can assign keywords and tags to the document, and it produces a graph that links it to every other document that you have in Obsidian; for example, if I have 17 dreams that I've tagged with "space travel", those 17 dreams are going to be linked to each other in the graph. It's really quite amazing. Obsidian uses markdown files and syntax, so it's compatible with every other markdown editory software (Pandoc, Deepdwn, Ghostwriter, etc), and can even be read in plain text.
I assign tags based on the themes or events. As aforementioned, space travel. This includes dreams on a planetary colony or on a space station; I'm not literally "traveling" through space but it's right in the same ballpark. I also dream a lot about androids or robot people, and I have had multiple dreams about living under the ocean, and multiple about living underground. So I might tag these "space travel", "space station", "androids", "underwater", "colony", "underground". Obsidian will link all of these documents based on their tags, and I will be able to see if I have a common theme between all the dreams I've recorded.
Lastly, I review my dreams every time I get deja vu. I get deja vu really often, and I made a habit of writing down exactly what I'm doing each time it occurs. It occurred recently when I was typing a message about various things, including Wordstar 4.0, and my keyboard. The person replied, "it took me too long to understand GRRM" and I felt like I could have sworn I had received the exact same message before in the past. I wondered if it was a dream, so I cross-referenced my dreams and found that I DID have a dream in which I was talking about a keyboard, though it was a different keyboard, and there was no mention of GRRM. Perhaps the deja vu was from that dream, and the fact that I had drempt it in the past had led to its occurance.
I have detailed this system here diligently because my hope is that you, too, dear noder, can discover the joy of cataloguing dreams. It's become a genuine hobby of mine and I greatly enjoy learning these things about myself, even if they serve no pragmatic purpose. Please tell me if you implement this system, or already do something similar -- I would love to hear about it!!