Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I have had Dock disappearance on me numerous times and for no reason.
Try this:

1. <Command+SpaceBar> will open spotlight
2. Type Monitor and select "Activity Moniotor".
3. Select "Dock" from the list of running Apps and then click the "STOP SIGN" button which is actually Quit Process and reconfirm "Quit".
4. This shall restart your Dock pannel.

Good luck.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.