Laryngitis occurs when the larynx, or voice box, becomes inflamed or infected, usually due to common cold, influenza, or more serious upper respiratory infection. When the vocal cords become infected, the tissue swells to cause obstruction of sound and air. The result can be anything from slight hoarseness or raspiness to complete loss of voice. Other symptoms may include soar throat or mild fever.
Should you suffer from laryngitis due to cold or stress, rest your vocal cords--don't even try to whisper. Keep your throat hydrated by drinking lots of fluids, sucking on throat lozenges (cough drops), and perhaps running a humidifier. Also, try to avoid smoking or being in any environment where the air is polluted (whether by smoke, smog, fumes, etc.).
If you experience prolonged laryngitis, it is wise to see a physician for diagnosis and treatment. Laryngitis can, albeit rarely, indicate more serious health problems such as pneumonia, polyps, or croup.
Some information found at Yahoo! Health.