You have a coworker with a serious personality disorder who's gone from feeling hostility/resentment to acting out and this is serious. Do report to some authority in your company and have witnesses in that discussion other than his boss who could take his side and distort your report to make you out to be sick. In my employer the HR rep offers different forums to explore charges: aggrieved and her boss and HR, aggrieved and charged and both bosses, bosses only, etc. i hope you have an outlet for addressing this situation and choices that make you feel secure. You have a right to that.