Research repeatedly points to the magic figure of 6 hours of sleep per night as the threshold where all sorts of bad stuff starts to happen. For example, Dr. Aric Prather, a leader in psychoneuroimmunology research from the University of California, San Francisco and his team found that if you drop your sleep to 6 hours or less for as little as 5 days in a row, you are 4.24 times as likely to catch the common cold.