Why do I automatically wake up when this happens, but can sleep through a thunderstorm?

Luckily the power didn't stay off for long and was back on by the time I woke up for good.

Something like the refrigerator is humming and when it shuts down you wake up! I'm glad it wasn't down for long!

Bummer.

I kinda woke up as the air conditioner in our room went back on. Any idea how long it was out?