The posture in which one experiences tremendous happiness and joy has been named Sukhasana by Yogacharyas. It is not any special asana. The posture in which one can experience happiness despite being in it for a long time is Sukhasana.
Sukhasana (Pleasure Posture)
Method
Sit cross-legged on floor. Right calf muscle presses down on toes of left foot and left calf muscle presses down on toes of right foot. Keep spine erect. Place palms on each other and place them on heels. This is Sukhasana.
Duration
Initially practice this asana for a minute and then slowly increase time as per the requirement. Both the inhalation and exhalation should be slow and as long as possible.
Other Benefits
Regular practice of this asana helps to achieve control over sexual cravings, non-conductive tendencies of mind and aids in purification of sexual energy. It strengthens flow of vital energy in the sushumna and as a result a person journeys inwards thus progressing higher on spiritual path.