Started tailgating me and swerving in her lane, for reasons I do not understand. I was driving safely, going the speed limit, and I merged in front of her into her lane, but made sure there was adequate time for her to see my turn signal and adequate space between her car and mine. I saw her proceed to tailgate me, and scream and yell in her car. I could even see her flailing both her arms around not holding on the steering wheel, which is most likely why she was swerving so much. I cannot imagine being sober and that angry, but she did in fact seem sober. At least she was not drunk, but could've been taking stimulants or something that makes one hyperactive (and induces extreme bouts of rage). Either way, sober or not, she did that for 15-20 minutes, then when she got the chance, sped in front of me (still huffing and puffing and screaming in her car) and then drove in front of me because we were in pretty congested traffic. I was behind her for a couple of minutes as we were both stuck in traffic, then she took an exit and left. This woman should not have a license or be allowed in a car until she can calm down or is given medical sedatives.