Part of the existentialist frame of mind would have to be an avowed understanding of atheism.  The existentialist would not admit the presence of as divine power.  For the existentialist, admitting the presence of a divine force would be an example of "bad faith."  The lack of a divine force in consciousness puts all of the burden of choice on human beings.  Sartre, himself, makes this a primary condition of the existentialist frame of reference:

Atheistic existentialism, of which I am a representative, declares with greater consistency that if God does not exist there is at least one being whose existence comes before its essence, a being which exists before it can be defined by any conception of it. That being is man or, as Heidegger has it, the human reality. What do we mean by saying that existence precedes essence? We mean that man first of all exists, encounters himself, surges up in the world – and defines himself afterwards. If man as the existentialist sees him is not definable, it is because to begin with he is nothing. He will not be anything until later, and then he will be what he makes of himself.

This is where the essence of agony in consciousness is evident.  Another aspect of the existentialist frame of mind exists in this element of choice.  The idea of choice as being a part of consciousness is one in which individuals are poised between equally desirable, but ultimately incompatible courses of action.  For the individual immersed in the existentialist frame of mind, there is an absolute understanding that the painful nature of choice and freedom is revealed.  It is part of the condition in which "existence precedes essence."  The pain caused by such a state of being contributes to an alienated sense of identity, part of the existentialist frame of mind.  The individual is going to be separate from their social order on two levels.  The first is that choice is an agonizing sense of being in which individuals must endure pain on their own and the second is that choice is often coming at the cost of social norms of identity.  In both, alienation becomes part of the existentialist frame of mind and reference.