Thankful to say, no, you haven’t broken your instrument and it won’t need an expensive repair. Bridges on violins, violas, and cellos are not glued down to the body of the instrument, they are simply held there by the tension of the strings. If your instrument has received a knock, occasionally the bridge will collapse. To fix this the bridge must be set back up in its original position. This really should be done by a professional as there are defined directions and positions in which the bridge has to be to ensure the best sound from your instrument. In the meantime pick the bridge up us as best you can under the strings to retain some tension and prevent the soundpost falling – or worse still a soundpost crack.