*raises hand *
Being alone in dark rooms, too. I, however, have similar difficulties with being alone in dark cars. Not as severe, but pronounced enough. I have dark-room trauma, but not dark-car trauma, so I think the only connection really is the "being alone in the dark in an enclosed space".
I don't panic, but I do tend to freeze and tense up. Like you, crossing the room to find the light switch...major endeavor. Takes all I have to pull myself together enough.
Things that are extremely hard are automatic lights that turn off while I'm in the middle of doing something, like walking down in the basement or down a hallway...that's even harder than if I was say on the couch or in bed and at least in a somewhat defined space and not stuck in the middle of the room. Power outages at night, too, because they come without warning -- for other situations I can at least prepare myself mentally.
Weirdly enough I often have no problem getting up at night and walking into the bathroom or kitchen in the dark...but I do sometimes get the trigger-senstation halfway through, as if my brain lags behind my body (movement). It does help to have night lights throughout, though. The darker it is, the less likely will I be able to do it/the faster that catch-up happens.