Why does it make me anxious when I confront someone?

A lady who lives nearby (who used to harass us) was staring at me from her car a few yards away. Her head was literally turned like an owl and she had fixed her gaze on me, unblinking. Once I noticed her, I looked away, a few seconds I noticed her again, looked away, finally the third time we locked gaze, and I kept staring at her unblinking too. About ten seconds later, she got pissed, scowled and finally drove away, breaking the gaze.
I got palpitations right after and my knees became wobbly, I got nauseous. It’s been more than 30 minutes now and I’m still anxious. Is it because I’m weak? What if she starts harassing us again because of this?