Matsyasana (Fish pose)     
1. Stretch the legs out fully in front of you while sitting.
Note : To fully gain the benefits of sarvangasana and Halasana it is important to practice Matsyasana.
1. Bend the knees.
2. Place each foot on the opposite hip joint, crossing the legs.
3. Now, lay backward, supporting yourself with your elbows.
4. Lie down. Let the legs, hands and head touch the ground.
5. Rest your weight on the elbows.
6. Bend the head well back so that the neck and back are arched up. Catch hold of each big toe with each hand.
7. Keeping the eyes open, retain this pose.
Breathe slowly and deeply. Gently leg to the grip on the toes.
Bring the back down unclasp the legs from their folded position.
  Sarvagnasana and Halasana must be followed by Matsyasana, because it is a complementary asana for both.
  Do this asana for half of the time that you do Sarvagnasana.
This balances the forward bend and backward bend of posture.
It also brings balance to the spinal cord.
This posture cures stiffness and pain in the neck, chest, legs and waist.
It relieves headache, pain in the eyes, ears and tonsils.
These organs get increased blood supply from this asana.
6. The rib cage and lungs expand, increasing lung capacity.
7. It helps in the practice of celibacy.
8. It increases concentration and purifies the mind.
9. It also helps in eliminating nocturnal emissions and nerve weakness.