Toyota Tercel - headlights came on by itself while parked, and making buzzing sound

I was woken up and informed that my car was making a buzzing sound, and that my headlights were
on. I went outside checked car - no sign of entry, and light switch was off. I started car (started
easily), and headlights remained on and buzzing noise continued after my ignition was turned off. I
ended up disconnecting the battery to get lights and buzzing noise to stop. The car had not been
driven for five days before this incident, and noone had been inside car. I'm mystified, can anyone give
me a clue what is going on with it?