Excellent pose when feeling pain or heaviness in the legs and pelvis during menstruation.
Make sure you are not arching your lower back by sitting on a small blanket, or pillow, and using it to lift the front of your hips higher (you want to have an angle of less than 90° between your legs and your torso).
Lengthen your spine.
Draw your arms behind, fingers tips pointing towards the front and gently bring the shoulder blades together to open the upper back.
Use a pillow or bolster against the wall for more comfort in the back.
If it feels good, you can also open the feet wide, following the same indications.
Breath fully and softly, all the way to the belly. if you have period pain, focus on your breath travelling to that area and visualise the pain as a dark light going away when you bring new fresh oxygen to this part of your body.
Stay in this pose as long as it feels good and then, go into a child's pose or Savasana, connecting with your breath.