I remember getting a similar shock, not this exact drop, but enough to feel the floor fall out for a minute. Sobbing after a bad test is a completely normal reaction, by the way, not an overreaction.
Here's the thing that's actually interesting in what you wrote: your two usual strengths, Verbal and DI, both landed at 77 on the same day. When one section drops you can chalk it up to a rough patch. When both of your strong sections drop by the same amount on the same day, that's less about content and more about state, adrenaline, the online proctoring environment, a slower start than usual eating into your pacing. The mocks measure skill in a low-stakes room. Test day measures skill plus everything your nervous system does to you at 9am with a webcam pointed at your face.
Give yourself a few days before deciding anything about a retake. Right now you're deciding from inside the disappointment, and that's rarely the version of you that makes the clearest call. When you're ready, it might help to talk through exactly what those DI and Verbal sections felt like in the moment, timing, nerves, anything unusual.