The word 'Matsya' would mean fish. This posture is named after one of the incarnation of Lord Vishnu who assumed the form of a fish. Hence the name 'Matsyasana' or the 'Fish Pose'.
1.Sit in Padmasana (Lotus pose)
2.Lie with your back flat with the legs placed on the floor.
3.Breathe out and arch the back, lifting the neck and the chest.
Taking the head back, rest the crown of the head on the
floor. Increase the back arch by dragging the head further back by holding the crossed legs.
4.Remove the hands from the legs. Flex the arms and hold the elbows resting the forearms on the floor behind the head.
5.Stay in this position for about half a minute to a minute with deep breathing.
6.Rest the back of the head on the floor and lie down flat on
the back. Breathe in and get back to Padmasana to release the
legs and relax.
7.Recross the legs the other way and repeat the pose the same
way for the same length if time.