I have lots of memories from things that I didn't really know were from dreams. I know now, that they were from dreams, but the memories themselves just don't seem to have a source.

I know that you have several dreams per night, but you don't remember most of them.

Maybe you DID remember those dreams, but only subconsciously, and (much) later, something made you recall them.

For instance, I have lots of memories from metroid games that don't really exist. They just seem to exist without a source.

Sorry, this is really hard to explain. It's actually pretty fun seeing what you can remember about dreams you don't remember.