Falling through Floor Into Water: Dream meaning and guidance

"I was walking through a house I didn't recognize, looking for the bathroom. The hallway kept getting longer, and the floor felt slightly soft under my feet. I remember thinking I should turn around, but I was already late for something. Then one of the floorboards gave way. I fell straight down into freezing water. I don't know how deep it was. I could see the underside of the floor above me, with a rug still lying over the hole, and I kept trying to reach it. My clothes felt heavy almost immediately. I wasn't alone down there. A shopping cart was sinking beside me, filled with random things--bananas, a lamp, someone's red backpack. I grabbed the backpack because I thought there might be a phone inside, but it was full of sand. The water suddenly became clear, and I could see a staircase below me. I started swimming toward it even though I knew it went farther down. At the bottom was a dry living room with a television playing. A little girl was sitting on the couch. She looked up and told me I was supposed to stay underwater until the lights came on. I tried to ask what lights she meant, but I woke up before I could speak, gasping and reaching for the edge of my bed. "