Waking up in the middle of the night and being unable to return to sleep is one sign of insomnia. But a recent story on NPR’s “Morning Edition” suggests that this wasn’t always the case.A period of wakefulness in the middle of the night used to be the norm. At that time there were no lights to turn on at night. When it got dark outside, it was just as dark inside.A winter night can bring 14 hours