Workplace harassment and possible retaliation

I, 22 F, need some advice on how to handle a situation at work. I’m a research assistant in a lab, and I’ve been experiencing repeated aggression and harassment from a postdoc. I just started in December BTW. He’s been acting in a hostile manner—getting physically close to me, jabbing at my work, rolling his eyes, flaring his nostrils in frustration, ignoring my questions, and raising his voice unnecessarily. I’ve reported this behavior to my PI (Principal Investigator), but instead of addressing it, he told me that if my performance doesn’t improve in the next three months, I’ll be put on a Performance Improvement Plan (PIP). This feels retaliatory, especially since I was only trying to report a hostile work environment.

I’ve drafted a formal complaint to HR detailing these incidents, but I’m worried about possible backlash. Has anyone dealt with a similar situation before? How did you navigate it? Should I expect HR to take this seriously, or is there a chance they’ll just side with my PI?

Any advice on what steps I should take to protect myself and my job would be really appreciated.

Thanks in advance!