Same dream for days?

I get home and go to our pool and my sister-in-law comes out of the changing room. I see her in her black, very tight swimsuit and she goes into the water. She dives under and I watch her. After less than two minutes she surfaces but doesn't come back up and twitches a little. She slowly sinks to the bottom of the pool. I jump in and dive towards her. I try to pull her up but she's stuck. After a few attempts I give her some air, then the dream is over and I wake up. What does this mean?