A question came up in yoga class about why we always roll to the right after Savasana. It turns out there are a variety of reasons why we roll to the right:
The right side is auspicious
Rolling to the right has a symbolic basis. In India, it is considered more auspicious to enter a holy place with the right foot, and in many parts of the world, we extend our right hand in greeting (in grade school, I remember being taught that we use our right hands to greet others partly because most of us are right-handed, but also because we are exposing our hearts to others). The right side also represents the east; rolling toward the east, or the rising sun, symbolizes asking for blessings, grace, and bliss.
There are physiological reasons for rolling on the right
Since the heart is on the left, rolling to the right puts less pressure on the heart and helps allow the blood pressure reach homeostasis.
Some believe that the right side corresponds to the cooling channel (ida nadi) which would keep the body in a state of calmness as it comes into a sitting position. Physiologically, the sympathetic (active) nervous system is thought to be associated with the right side of the body, and the theory is that by rolling to the right, the meridians associated with the sympathetic nervous system helps stimulate wakefulness when coming out of Savasana. But I believe this is an oversimplifcation of what is really going on in the body (otherwise how does anyone sleep on their right side?).
The most important thing to keep in mind about coming out of Savasana is this: an appropriate Savasana provides the room for the student's nervous system to shift to a state of ease (lower heart rate and blood pressure, stimulation of the digestive processes, lower body temperature, release of endorphins). Students should come out of Savasana gradually, slowly, with no hurry or jarring action. Additionally, rolling to the side and pressing the floor helps prevent tension in the neck and lower back.
... but it depends!
So, we roll to the right after Savasana. But like everything, it depends. Pregnant women should lie on their left because it makes the heart's job easier as it keeps the baby's weight from applying pressure to the large vein (called the inferior vena cava) that carries blood back to the heart from the feet and legs. Lying on the left improves circulation to the heart and allows for the best blood flow to the fetus, uterus, and kidneys. Since the liver is on the right side of the abdomen, lying on the left side helps keep the uterus off that large organ.