Scary nightmare about a dark basement... what does it mean?

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Had a dream a while back that I was approaching a house in broad daylight, it was nice, sunny and calm. I walked to the side of the house where there were a pair of cellar doors. I opened them and entered the basement. It was dark, murky, had a rusty tint to it. I entered some sort of dark broken down bathroom that was kinda spacious and had a closet inside it. As soon as I entered, I felt like something was coming for me. I turned and something tried to get in the door behind me, I immediately screamed and held it back. I couldn't make out what it was but I knew it would be horrifying in my eyes. Soon I lost my strength and the door flung open and the figure was revealed -- a demonic woman with long hair, piercing eyes, and a patch of flesh covered her mouth as if it were a piece of mold. The ceiling light shined brightly behind her, almost obscuring my vision. I woke up saying No over and over again. What on earth does this dream mean? I've gone over and over it so many times, I know the basement has something to do with the past, but I can't figure out anything else beyond that.