I think the trouble is that if you are having nightmares and are plagued by horrid memories etc etc etc and thinking of taking sleeping medication because you can't sleep...

Then the last thing that is needed is for you to dwell on painful stuff and / or bring up painful stuff in therapy.

If you aren't coping then you need to learn coping skills so that you are better able to cope when the hard stuff does come up in therapy.

Are you able to do a DBT program at all? DBT focuses on giving you skills like mindfulness, emotion regulation, distress tolerance, interpersonal effectiveness. Linehan suggests that clients learn the skills for a year so that they are fairly automatic BEFORE getting in to trauma work. So... Where you are at isn't that unusual. But.... It might be worth thinking about changing your focus to getting good coping strategies than some painful blend of talking / thinking about trauma and seeking out (potentially addictive) sleeping medications to sedate you into forgetting...