Your pillow is probably disgusting, which means it's time to wash it. To do so, Apartment Therapy suggests rolling it up tight and securing it a rubber band.
Picture: Quinn Dombrowski/Flickr
Basically, you want to minimise the chance of the synthetic fibres clumping up. So, roll the pillow lengthwise, then secure the ends and middle with some rubber bands, and toss it in the washer with some liquid detergent. When it's done, lay it flat to dry.
How to Wash Your Pillows [Apartment Therapy]