Octopus cave

I don't remember the whole dream even though I know that it was significantly longer. This is the end part.

I'm in a cave filled with a air-water-hybrid substance. Breathable, clear, room temperature, but slow to move in and gravity-reducing. The cave is fairly high and well-lit. The floor resembles a sawtooth wave . There are octopuses swimming in the air. I'm not alone, there are many other people trying to get to the other end of the cave. My little sister starts running to the other end, and I have to catch her. As I jump over the sawtooth peaks an octopus grabs my arm. It feels very cold and uncomfortable, and my arm goes numb. I manage to tug myself away from the grip and continue jumping. My sister has dissappeared and the octopus is chasing me. I see a small hole in the wall in the end of the cave. I crawl through the hole, it leads to a wooden tool shed built inside the stone. I wonder if the octopus will follow me, but suddenly something breaks through the wall... and I wake up.