Just the other day I was running a whole load of applications on my Macbook Pro, and I saw my memory usage and CPU usage spike up (it was due to a couple of Adobe AIR applications – Mac OS tends to be bad at running Flash and AIR). And right about then, I had leave, so I had to put my Macbook to sleep. Later, when I tried to wake up my Macbook, I found that my dock had disappeared and I couldn’t bring it back up. Using cmd+tab still worked and my various applications were still running fine, so I knew that it was a problem with the dock.
So I tried killing it with the following command. Just open Applications>Terminal, and type in the following command:
killall -KILL Dock
What this command does is to kill the dock process, and restart it. Voila – you now have a working dock again!