Tatastha-sakti is a "fallen condition" of the jiva-souls.

Tatastha-sakti is a "fallen condition" of the jiva-souls that refers to those who are "conditioned" in the temporary material creation, and those "inactive" in the impersonal Brahmajyoti, who had entered that "dormant" state to escape the frustration and suffering of repeated birth and death within the material world. 

This temporary nature of the material world causes the trapped jiva-souls to attempt to put an end to their existence by entering an "inactive" (dormant) state of consciousness within the impersonal Brahmajyoti. 

To a Vaisnava entering the impersonal Brahmajyoti is Spiritual suicide.

Even those who do achieve merging as as individual unit into the inactivity of the impersonal Brahmajyoti, does not destroy the jiva-soul who is eternal, it only temporarily leaves them in an inactive state of consciousness for a very, very, very long time.

So long that when the jiva-souls eventually falls out of the impersonal Brahmajyoti, they foolishly believe that the impersonal brahman or Brahmajyoti is their origin. 

They do not see that the material manifestation, the impersonal Brahmajyoti and tatastha-sakti are already fallen conditions of the jiva-souls they had previously fallen too.

Entering the impersonal Brahmajyoti is only a temporary state of inactivity, all jiva-souls eventually enter back into a material bodily vessel within the material creation. This is because the eternal nature of the jiva-souls is to be always "active." 

Ultimately serving Krsna the Supreme Personality of Godhead and cause of all causes, leads the jiva-souls out of the temporary decaying material world and back home back to Godhead.

Tatastha-sakti refers only to those marginal living entities (jiva-souls) who are already in a fallen condition in the temporary material creation.

And includes those jiva-souls who have become further frustrated by the temporary nature of material existence and the suffering of experiencing repeated birth and death, causing the conditioned jiva-souls to attempt to put an end to their individual existence by entering a dormant (inactive) state of consciousness called the impersonal Brahmajyoti.

In other words, tatastha-sakti does not describe those jiva-souls in their original "none-fallen" position in Vaikuntha and Goloka Vrindavana.

Tatastha-sakti is a name describing the none Krsna conscious condition of the fallen jiva-souls.

Srila Prabhupada - "So this temporary material world is the taṭastha (materially conditioned) characteristics, and the spiritual world is the permanent (personal) characteristics. So our effort is to get out of this taṭastha (materially conditioned) characteristics and enter the permanent (personal)  characteristics. That is called spiritual elevation." (Lecture on CC Madhya-lila 20.354-358, New York City, Dec 28, 1966)

Srila Prabhupada - "Because the individual soul is apt to fall down sometimes under the clutches of māyā, it is called taṭastha-śakti. Just like in the seaside the shore, the beach, sometimes you see it is covered by water and sometimes it is land.

Similarly, when we are covered by māyā, that is our jīva-bhūta stage (which means struggling under the laws of material nature), and when there is no more material covering, that is brahma-bhūta stage (realizing you are the jiva-soul above material influence)  

When we are Kṛṣṇa conscious, then we are brahma-bhūta (SB 4.30.20), and when we are not Kṛṣṇa conscious, we are materially conscious (jiva-bhuta), that is māyā." (Lecture on BG 7.4-5 - Bombay, March 30, 1971)

The marginal living entities or jiva-souls are not called tatastha-sakti in Vaikuntha or Goloka Vrindavana as Prabhupada explains above because the word tatastha-sakti is a "conditioned" designation. 

In Vaikuntha and Goloka-Vrindavana the jiva-souls are not in the conditioned state and therefore not called tatastha-sakti.

The word tatastha-sakti refers to the marginal living entities (jiva-souls) in their fallen conditioned state in both the material creation and when dormant in the (impersonal) Brahmajyoti.

Revatīnandana - "Srila Prabhupāda you very clearly explained to me once in a letter that if the jiva-soul then goes into the brahmajyoti, he is considered still fallen. Still fallen. Does that means the whole brahmajyoti is composed of fallen souls? You see my question? If I go there, I'm a jīva-soul, and I go to the brahmajyoti I'm still fallen."

Srila Prabhupāda - "Yes."

Revatīnandana - "That means all jīva-souls there in the impersonal Brahman (Brahmajyoti) are also fallen souls?"

Srila Prabhupāda - "Yes, existence in the impersonal brahman is also within the category of non-Krsna consciousness. Those who are in the brahman effulgence are also in the fallen condition, so there is no question of falling down from a fallen condition. When fall takes place, it means falling down from the non-fallen condition (Goloka-Vrindavana and Vaikuntha). The non-fallen condition is Krsna consciousness.'' (Letter to Revatinandana, LA 13 June, 1970 and 1971 London)

The jiva-soul's original position in Goloka Vrindavana from where they originated from, have the same bodily features as Krsna.

The full potential and original feature of all marginal living entities is a two arm form like Krsna's Body Prabhupada explains.

Devotee – "Is the original body of the spirit soul a human form?"

Srila Prabhupada – "Yes, human form. God is also human form. "Man is made after the shape of God." I think there is in the Bible. Is it not? So God is also like human form. Here you see Krsna, two hands, two legs."

Hari-sauri – "How do we understand, then, that there are peacocks and flowers and trees in the spiritual world? Are these not eternal forms?"

Srila Prabhupada – "[describing material form first] Yes, they are more covered, just like if you cover your body with blanket, the hands and legs are invisible. But you are not the blanket. So the trees and plants, they are more covered. They are not in full manifestation. The human form is the full manifestation of the soul."

Hari-sauri - "Are they covered in the spiritual world?"

Srila Prabhupada - "Not in the spiritual world, there that is voluntary. Some devotee wants to serve Krsna as flower; they become flower there. If I want to be a flower I shall lie down at the lotus feet of Krsna and become flower, voluntarily, and can change from flower to human body if one desires. That is spiritual life. There is no restriction. If some devotee wants to serve Krsna as cow, he serves Krsna as cow, as calf, as flower, as plant, as water, as ground, field, or as father, as mother, as friend, as beloved, anything. It is inconceivable, yet a fact." (SB 6.1.1-4 - Melb, May 20, 1975)

As said above the word tatastha-sakti refers to the marginal living entities (jiva-souls) in their fallen conditioned state in both the material creation, and when dormant in the impersonal Brahmajyoti or Brahman only.

It is foolish to believe the jiva-souls originate from tatastha-sakti (a conditioned fallen state) Srila Prabhupada explains.

The marginal living entities (jiva-souls) sometimes fall down to the material creation from Vaikuntha or Goloka-Vrindavana which are their original homes.

And then after being frustrated in a material body trapped in the cycle of birth and death in the material creation, they attempt to find escape by entering the impersonal (inactive or dormant) Brahmajyoti. 

The fact is the jiva-souls do not originate from the Impersonal Brahman (Brahmajyoti), the Body of Maha-Visnu or tatastha-sakti (a conditioned designation) as some believe.

ALL jiva-souls (marginal living entities) are eternal and come to the material world from the Vaikuntha planets and Goloka Vrindavana.

Srila Prabhupada - ''Existence in the impersonal brahman is also within the category of non-Krsna consciousness. Those who are in the brahman effulgence (impersonal Brahmajyoti) are also in the fallen condition, so there is no question of falling down from a fallen condition. When fall takes place it means falling down from the non-fallen condition. The non-fallen condition is Krsna consciousness [Vaikuntha or Goloka-Vrindavana]." (Letter to Revatinandana, LA 13 June, 1970)