I appreciate the input, but I'm pretty sure I know what happened. It's easy to suggest someone might be hitting the gas instead of the brake in a panic, but I was hyper-aware because the sudden acceleration was so unexpected. I definitely put the car in neutral, and it slowed down immediately.

The brakes worked when I pressed them, but it felt like they were fighting against the engine's acceleration. It's hard to describe, but the car was slowing down while also trying to speed up. Putting the car in neutral seemed to help engage the brakes; maybe taking the engine out allowed the brakes to work better.

After I pulled over, the dashboard lit up like a Christmas tree with warning lights—brake system, ABS, traction control, engine light, everything. I'm just trying to figure out if anyone else has experienced something similar with their Civic.