At work today, my boss slapped me, what can I do?

First time on a q&a site with a serious problem so only serious answers please…I was at work today (Sunday) because I was asked to come in to help with a project. My boss became upset with me because she didn’t like my final powerpoint and after some yelling she slapped me across the face. I was stunned and since it is Sunday, HR was not in the building. Also it happened in her office and nobody else was there so I have no witnesses.

Anyone has any idea what you do in such a situation? I haven’t told anyone so far and I’ve just joined the company 5 months ago and it’s a different line of work than what I did before so ideally I’d stay longer to build experience before I can look for other jobs in the same field. It’s not the first time she’s been yelling and I pretty much go to work everyday with a big knot in my stomach but I put up with it up till now because this job opens good options for the future, but after this I’m not sure it’s all worth it anymore.