Watch a funny cartoon, and if your a Christian read John 14:27 in the bible. It states "Peace I leave with you; My own peace I now give and bequeath to you. Not as the world gives do I give to you. Do not let your hearts be troubled, neither let them be afraid. Stop allowing yourselves to be agitated and disturbed; and do not permit yourselves to be fearful and intimidated and cowardly and unsettled". I always read that verse when I watch something scary/disturbing. It calms my heart.
If you still can't get it out of your head, just tell yourself "Ill completely forget it in a month or two."