I had the same problem (never being able to get any type of "rested" bonus) and discovered that was a stuck quest called
Since nearly every scripted activity in Skyrim is a "quest" of some sort (at least internally), it's possible that a previous execution of the script did not complete properly; I've found this can happen from a crash or even using "qqq" from the command shell to fast-quit. Additionally, you can only have one instance of any given quest active at a time.
Luckily the solution is pretty simple:
- From your current game, use the ~ key to enter the command
- Type help PlayerSleepQuest to get the questID. It should be 000FC1A2, but if your's is different for some odd reason, then be sure to use whatever ID is shown for the remaining steps.
- Type stopquest 000FC1A2 (press Enter)
- Type resetquest 000FC1A2 (press Enter)
The next time you sleep, the PlayerSleepQuest should activate properly and provide the appropriate feedback on screen and be shown in your active powers list.
(Disclaimer: I have absolutely no idea how doing this might interact with any currently active Lycanthropy or Vampirism character state! Be sure to have a good/known save to revert to should things go haywire!)