What it says up there. In my 2015 Prius 3, I was driving on the highway and to make my exit I had to brake pretty hard, and immediately after the check hybrid system warning lights came on along with the check engine light, traction control/abs light, the glowing triangle of doom, the whole nine yards. Drove a few blocks to a safe spot and turned off the car. Turned it back on and the lights were still there. I'm going to check on it in a bit and see if the warning lights are still there, but I'd like to solve this myself given that the dealership that has the warranty is in the next town over and I don't want to drive it that distance or pay to have it towed that distance.
you can try reading the codes, then resetting them. might be a bad speed sensor or stuck caliper or something. codes will tell you. post them here before resetting.
If it is still under warranty and under 150k miles, take it to the dealer. I have seen brake boosters go out after hard braking.