I would do what Elegran says sunseeker we often find the lounge lights on and are sure we switched them off ( but obviously didn't.) You scratched yourself during a dream, so cut your nails very short.
If really odd things continue happening, consider having a cctv type monitor in lounge and bedroom ( you can get it set up for you) but only if more than this occurs.
Christmas and New Year can be a stressful time when you live alone.
When you are ready to go to bed, go round switching off the lights and locking doors and say out loud, I am switching this light off ( the only way to insure that you have done it, rather than mean to do it.)