I have a 2004 Chevy Avalanche.  Last night, I drove into my driveway and turned
the ignition switch to off.  Immediately, there was no electrical activity at
all: no lights, no radio, turning the key to start produced nothing.  Because I
park outdoors and it was very dark, I decided to wait until morning to diagnose
the problem.  

This morning, I opened the vehicle door to pull the hood latch, and I saw the
dome light on!  Hmmm, I had electricity.  Using my digital voltmeter, I measured
the battery voltage at the battery terminals and got 12.56 volts - fully
charged.  
I turned the key, and the car started and ran perfectly.
Later today, the electrical was still working.

What could have happened?

Is there some inline circuit breaker which overheated, cutting all electricity
until it cooled down?