(((((((dreamland))))))
Having been inpatient several times I know that you can get a lot of work done. It's intensive, but it keeps you safe while working through things. I also have gotten a LOT just out of being with others that have similar diagnoses as I do, really makes you feel not so alone. And, sometimes, there are some fun times and there's a lot more laughing than one would "expect" at a psych hospital (of course, along with those tears). Will you be going to a facility that specializes in DID/trauma? You can learn a lot.
Good luck, and try to not be too scared...it's really not that bad.