How cold is too cold while sleeping? Nights have been getting down to 38 degrees, yet when I am in California, I still sleep with the two biggest windows in my bedroom fully open. I have blinders over the bottom half closed, but the top half are open. And they aren't the cheap plastic type of blinders that Middle Class Murox has on his $340k house, so my blinders keep a lot of the cold air out, but the 38 degree temperature still has the room very cold. Since I have family visiting, I keep the rest of the house between 71 - 72 degrees, but what temperature is too cold to sleep in?