Electrical problem with headlights

Tonight I parked my car. The headlights were on auto as usual. When I came back to my car about two hours later, I noticed the following:

1) Headlights were on. Running lights were on.
2) I checked the position of the headlight switch. It was still in auto mode.
3) I had to turn the headlight switch to "off" for the headlights and running lights to go out.
4) There was not enough battery power left to start the car.

I left the car alone for about an hour. Enough juice returned to the battery to start it. I drove it for about 20 minutes with no issues. When I got home, I performed some additional tests:

1) I put the headlights back on AUTO. They did not go out when I turned the car off and locked it. I had to turn the lights off manually.
2) When the car is running, the car will lock and unlock from the driver's side electric switch. When the car is OFF, the same switch will only LOCK the car. To unlock it without the engine running, I had to manually unlock the door.

Based on this information, what do you think is going on?

Thanks in advance!

John