My boss sent an email saying that My timesheet was wrong. It was. But, he put down that I was at an Oncology appt. the whole office knows. can I sue?

Hello, My boss recently sent an email stating that my time sheet was wrong. It was, wrong code for time out of the office. He sent an email saying that the sheet was wrong and the reason I was out was because I was at an Oncology Appointment. My co-workers didn't know that's where I was. I had texted him with that information the previous week, because I thought as my boss he should know. Now, my co-workers are asking, what's wrong? what type of cancer? etc. I feel violated, hurt and quite honestly, I can't afford to quit and go someplace else. I've read the hippa laws, and it seems like I can sue, but this guy doesn't seem to care.