Thanks so much for your advice! It must have been a problem with the master cylinder because the brake pedal completely sank to the floor a few days earlier. My brother replaced the master cylinder, flushed out all the old brake fluid and added new. He showed me the level he had filled it to so I can keep an eye on it the next few days... just in case. The brakes worked fine on my drive home but I'll drive cautiously and leave plenty of room ahead of me until I regain my comfort level.

I feel more prepared now knowing the different options for slowing and stopping if the brakes fail again.