Wow! As someone else said above, you worded this perfectly. I've tried to pin this down I don't know how many times, and it didn't come out right.
For me this is like a full time occupation, I don't mean 12 hours a day, I mean 24 hours a day, when I'm dreaming, when I can't sleep, when I wake up. Like someone else mentioned, don't know how I function at all... or have real relationships with people, I'm never here. I can barely pay attention to what's going on around me. I am hideously self-absorbed. The only way it will stop is if I take OCD meds (Anafranil or Luvox), klonopin and ritalin.
Anyway, right now it's my primary source of distress. I am pretty dissociated from it (excessive introception = derealization/detachment from world, kind of like a permanent state of zoning out) and paired with depression, all of the imaginings become anxious and painful.
I had an OCD specialist call it 'compulsive mental review'. It is a compulsion, not unlike washing hands or checking knobs, but internal one, used to soothe background anxieties/turn off the "something's wrong" alarm in the body.
I joined the 'maladaptive daydreamers' group but couldn't be bothered to read all the posts since I was too busy imagining interactions. I personally consider it a dopamine addiction. Instead of using exogenous chemicals, I use endogenous ones through the imagining of social reward. My brain doesn't really know the difference. Unfortunately, it all goes bad with depression.
Thanks for expressing this so well. It really helps.