Kris's turbo

My wife was driving the accord and she said the engine rpm went to 7000 and the brake pedal felt like a rock. What could cause this I thought it could be a hole in the brake booster hose but I checked it and it was fine. A little while later the car ran fine but it's the second time this has happened. Anyone know what could cause this, maybe the check valve in the brake booster hose?