A sashtang namaskar is a type of namaskar in which all “angas(body parts)” touch the ground. As such, this type of namaskara is also called “dandakara namaskaram”, “uddanda namaskara”,etc. The word “danda” means “stick”. The dandakara namaskaram is one which in which the person simply lies on the ground like a fallen stick. This is done because a fallen stick symbolizes ‘helplessness’, i.e it is a way of conveying to the Lord that you are as helpless as a fallen stick & have taken his refuge. It is a symbol of sharanagati in the Lord’s feet. This namaskara is also a form of destruction of ego. When we fall from a standing position, we get injured.
Even in a seated position one can get injured. But look at the sashtanga namaskar position. The is no possibility of a person falling at all & hence no question of injury. As the height increases, the fall becomes more severe. The fate of one in high position is also similar. If he does wrong, slips and falls, he is unable to even get up – that is recover to the high position.
The biggest load for a person is his ego-sense, the I-sense, the Ahambhava/ Ahamkar. There is permanent peace if that load is taken off one’s self. The namaskara kriya is the best aid for getting that load off ourselves. Hence, sashtang namaskar is a process of removal of ego & development of humility. If the head is brought down by others, it is a disgrace. If we bring it down ourselves, it is reward, honour.
This is vinaya sampath (humility that is wealth itself). It is to get away from “head weight” and mental conceit that the namaskara I performed with the head in the lowest position. Such a namaskara when done to a sanyasin/eders/guru means the the latter is a “carrier” of your prayer to god. The person receiving the namaskar must not be of the opinion that the namaskar belongs to himself. Instead, he must understand that he carries this namaskara towards the Lord & prays to the Lord for the welfare of the person doing the namaskar.