You should not get up quickly if your room is cold because your blood vessels are thin when it is cold and getting up quickly raises your blood pressure suddenly damaging your blood vessels. In the worst case, you could have stroke.
So before you get up, it is recommended to open and close your hands and feet for 30 times. (Fig. 1 & 2)
While we are sleeping, parasympathetic nerve is active. When parasympathetic nerve is active, blood vessels become larger so blood tends to gather in your hands and feet. Before you get up, opening and closing your hands and feet for 30 times makes your blood flow better. Since the blood flow of your brain gets better and your body gets warm, you can easily get up.