"Why do you keep your house so cold?"
Speaking for myself, and I am unanimous, sleeping in cool or cold is best way to go.
Studies have proven it is better to sleep in a cool or even cold room (provided proper bedclothes are provided) than a warm, hot or even over heated one.
Give me a chilly bedroom and nice eiderdown or series of blankets or quilts and will sleep like a log.
Idea of sleeping in a hot or even warm room is a relatively new thing, largely brought about by automatic heating.
Back in days of solid fueled boilers (including back boilers) or furnaces most homes, apartment buildings, hotels and pretty much everyone else "banked" fires for night. This both saved fuel but more importantly given lack of safety devices prevented a fire from starting overnight.
Someone had to wake up in a cold house or whatever, go downstairs or where ever boiler/furnace was located (or controls) and get fire going again so place would get heat.
Above assumed a place had central heating. If relying on fireplaces there wasn't heat in morning until someone got up and built up the fire.
Our grandparents were firmly old school, boiler was turned *OFF* at night. Needless to say oneself, siblings and cousins did our best to avoid sleeping over anytime during cool or cold weather.
Parents believed sort of same in that heat was turned down late evening/before house retired for night. All beds had lots of blankets and quilts so we kids never were bothered. Which ever parent was up first would turn up the thermostat so by time we kids were getting up house began to warm.
In dead of winter have valves closed to rads and window slightly open in bedroom.