I haven't looked for this statement in the manual, but there have been a number of owners that had cars "settle down" over parking stopper blocks when powered off and then rip the front bumper off when backing up, so I think there is anedoctal evidence that some cars at least will not self level when "asleep". Also a good reason to not park so close or to back in to parking spots.
Just a couple of weeks ago, I loaded about 450 lbs of cargo into the back of my Model S and noticed the tail sagging until I turned it on and it self leveled right after I turned it on. Again, suggests self leveling isn't active when off.