I went away for work and left my truck parked for 8 days. Went to drive it lastnight, and the highbeam light came on, and stayed on. The headlights are super super dim all the time, and when you do turn the highbeams on, the pass. side goes on, but the dim drivers side light turns off completely. I turned the headlight switch on and unplugged the bulbs one at a time, and no matter which one is unplugged, the opposite light turns off. Very odd...

 

IMO, most likely a failed dimmer (multifunction lever) switch or failed headlight switch. Both are fairly common. I'd pull both out and look for the obvious signs of melted wires or melted plastic, and replace whichever is damaged.

 

Fixed! I had installed some brighter bulbs, and I guess my truck didn't like them. Put plain old bulbs back in and everything is fine!