It's definitely not great when you can't touch your bottom ..
That's a really bizarre issue. Sounds like the hardware is fine given everything is working while in Settings.
Have you installed anything recently - a new app or ROM, say? If so, try uninstalling or switching back to what you had previously.
How are you fixed for free memory / storage? I guess it's possible you need to free some space.
This may be a case of sending the phone back for a warranty repair.