During that rough draft, be as vivid as you want. You can put anything that you feel fits into the story in your rough draft — that’s the glory of a rough draft. It’s in the editing stage that you’ll then be able to go through and decide if it needs toned down or not.
However, also keep in mind that having vivid dark themes is sometimes a good thing. Don’t be afraid of what you’re working with, whether it’s depression or marriage or fighting dragons. If you skirt the issue or feel uncomfortable writing it, the reader will notice.
So, don’t be afraid to put those strong emotions and images in there. You can always edit them until you find your balance!