Two-sentence horror stories can be quite scary. They often use simplicity and ambiguity to let your imagination run wild, which can make the fear more intense.
A different one could be 'The picture on the wall changed. It showed my gravestone.' This is really scary as it implies some sort of malevolent force is at work, changing the picture to something so ominous. It makes you question the safety of your own home and what could be causing such a strange and disturbing occurrence.