Do your windows look like this picture above? Whereas that is a gorgeous winter picture, if your plants are on that windowsill and actually touching the window, they will be damaged. When it is frigid outside, as it is going to be this week in the midwest, our plants need to be protected from the cold.
Cacti and other succulents will most likely be fine, with the exception of, at least in my house, the succulent group euphorbia, which inlcudes the crown of thorns. I moved my euphorbias off the windowsill above covered with ice, as otherwise they will lose their leaves. I have experienced this. Below are some euphorbias, that if they are exposed to cold temperatures, will drop their leaves.
Any plant that is touching a window when it is cold outside, may be damaged. Below are a few that will be adversly affected it their leaves are touching the window, or stunted by just being close to the window.
Move your plants to plant stands in front of the windows instead of placing them on the windowsill. Another way to protect them is to place a piece of cardboard between the plants and the glass when the temperatures are cold. Do your best to make sure your plants are protected and warm.
Have you ever had your plants damaged from the cold weather?