Headlight fuse?

OK, so it happened last night and I haven't even cracked the manual yet.
Just figured I'd jump on here because I'll be thinking about it all day at work until I can get home and look into it.

Truck was parked and I was using the spot lights on back of cab to illuminate the area that I was working.
After about 30 seconds the alarm for leaving the headlights on started chirping. No biggie, I knew what it was from past experience.

Fast forward 5 minutes and the spot lights went out.
Cab lights won't work.
Headlights won't work.

This makes me think they are all on the same fuse, and I burned it out.
Does this make sense?

I was plugged into shore power at the time, so amperage shouldn't have been an issue.

I think the only other times I used the back lights I had the engine running.