A State of Confusion and the Awakening  

Similar to the almost stunned state of someone who suddenly awakes from a deep sleep, the spirit, upon separation from the material body, experiences a state of confusion that obscures its perceptions and continues to experience an impression of matter.  The degree and duration of this state, anywhere from a brief, insignificant moment to a period of years, depend on the spirit's knowledge about the true meaning of death, its level of purification achieved thus far, and the degree to which the spirit freed itself from the grip of matter during its incarnate life¹.  

In addition, Kardec explains² the confusion often experienced by a spirit who undergoes a violent or sudden death, for example by suicide, capital punishment, accident, stroke, etc. He writes:

The spirit is often surprised, astounded, doesn't believe itself to be dead, and stubbornly persists in asserting the contrary.  Nonetheless, it sees the body it has left as something apart from itself.  It knows the body to be its own, although it can't understand how the body became separated from it.  It then goes about among its living friends and relatives, speaks to them, and becomes puzzled when they do not hear it.  This sort of illusion lasts until the separation of the perispirit and the incarnate body is complete, since only then does the spirit begin to understand its actual situation and realize it is no longer part of the human world.....In the case of collective death, in which many persons have died in the same catastrophe, it has been observed that they do not always see one another immediately afterwards.  In the confusion that follows, each spirit goes its own way or concerns itself only with those in whom it takes great interest.

Just like the degree and duration of this state of confusion, the experience of awakening and regaining consciousness in the spirit world depends upon the condition of the spirit.   For the spirit who lived honorably on Earth, the confusion will be brief and death may seem like a peaceful awakening from sleep; the sensation is one of a relief from a heavy burden.  However, for the spirit whose conscience is troubled by its wrongdoings, the sensation is one of anxiety, distress, and shame.

¹ evidenced by  the practice of goodness and and of a clear conscience
² See discussion to Question 165 of  "The Spirits' Book"