Before then, I had started having what I've dubbed "broken dreams" where symbols that mean little to nothing to me show up and wreak havoc in the dreams, usually ejecting me into consciousness from the shock and confusion. However, after that day, the rate of these events dropped drastically, and when they did occur, they were more "benign", in that they didn't throw me out of the dream in confusion and more just took the dream different directions. The foreign symbol invasions are what I suspect to either be external beings coming to "join in on" my dreams, the collective unconscious somehow affecting me, or who knows what else, but the external beings theory is the one that I most agree with at the moment.
A month or two later, I had a dream in which a catgirl appeared and attacked my dream avatar and a large number of NPCs with what resembled spatial magic, warping space into a bubble and trapping multiple NPCs inside. I say "spatial magic" only because that's the only parallel I can make to what it was, as in the dream I was just confused about what was going on. This dream prompted me to consult with my friend who also has weird dreams from time to time, and he ventured the possibility that I had unwittingly formed something akin to a tulpa (we use the word familiar, but much of the core details are the same). Curious to see if this had happened, I did a mental "anyone there?" and to my utter shock I received a response. Within a week the "tulpa" was projecting her detailed catgirl form into my mindscapes and interacting with me perfectly fine, leading me to believe I had unwittingly formed a tulpa.