Flies swarming in the old Bedroom

"I walked into a room that was sort of my old bedroom and the window looked wrong, dark and shifting, and it took a second to understand it was covered in flies, hundreds, stacked on each other, that low heavy buzzing filling the whole space. I didn't scream, just stopped dead in the doorway. They started coming off the glass in clumps, drifting toward me slow, then faster, and I backed into the hallway swatting at my face. One got in my mouth, or felt like it did, and I kept spitting even though nothing was there. The hallway was full of them too, crawling along the walls, along a lamp, all over a bowl of something on a table that hadn't been there before. I couldn't find a door that wasn't already covered, and my arms moved too slow to do any good. That buzzing got louder until I couldn't hear anything else, right as I felt them settling on my shoulders. Woke up shaking my hands out, brushing at my arms in the dark."