What is Critical_Process_Died?

I came back to my computer after leaving it for a while and when I looked at my screen it was black with a message saying I need to Restart my computer with a 0% next to it. The reason it gave was the error code Critical_Process_Died. Once I restarted the computer everything works and I am even typing this on my PC after it happened. What does this mean and should I be worried?