It helps to write/discuss them w/ some you trust to flesh things out. drowning sometimes signifies you're anxiety over something. an obstacle or trauma that may have happened in your life. If it affects you so much that you cant function during the day seek professional help. we are very vulnerable in our sleep, try to stay away from movies or shows that are graphic particularly the hours before you head to bed. that might help as well.
Sometimes, when you go to sleep either thinking about it, or something bad, you dream about it. If you go to sleep thinking about something you like, someone you like, or something good,you end up dreaming about it.