If you feel you are being harassed, look in your employee manual for the proper procedure for reporting harassment. Many workplaces (and the Equal Employment Opportunity Commission) state that you should speak with your boss first. However, with gaslighters/narcissists, this usually does no good, and can actually make things worse. Consider speaking with an attorney about your rights and what you should do next.
Consider leaving your job. Finding a new job creates a burden for you, but consider how your mental and physical health is being affected by this person. Also, what will working under this person do to your career? As one employee was advised in a New York Times column, you will most likely never thrive under this (lack of) leadership. You may find a better job, one that better suits your skills and needs.
It is also possible that the longer you stay at this job, the more opportunities the gaslighter/narcissist will have to hurt your well-earned good reputation. For many narcissists/gaslighters, once you leave the company, they disappear from your life. Gaslighters/narcissists rarely want anything to do with someone who is not present. It’s much more difficult to create drama that way.
When you are asked in interviews why you left this job, you can be truthful without giving gory details. A simple, “I was looking for a new direction for my career,” or “My values were not in line with the management” will usually suffice. You can also add a positive, such as what you learned from the position, or what contributions you made. Consult with someone in your field about how to best respond to interview questions about your previous job.
You can and will find better opportunities, ones that lift you up instead of calling you into question constantly.