Is death a conscious act? In the book, I come across a statement that says:


  Many theologians say that death is always "a conscious act, " even
  when we seem unconscious to those around us. It is an act we perform,
  not something we simply use undergo.


Is there any supporting proof for this statement within the Roman Catholic Church's teaching or where some theologians get that idea?
There is a understanding in Catholic Culture, that most people at the end of their lives, typically die in the same manor that they lived.  For example, A person who lives his life rejecting in his heart the idea of God, will at the end of that life, continue on as when he was living it.  Alternatively, a person who lives a sacramental life of Prayer and adoration will continue to do so at the time of their death.

Redemption, as understood by the Catholic Church, includes stages, initial acceptance into the Church by Baptism, the reception of the Blessed Sacrament and confirmation. Unlike the New Christianity where preachers teach that  if only "once" you accept Jesus as your personal Lord and Savior, you are saved.  Christ and his church teaches biblically that a person must persevere to the end.  It is also clear that even a saved person continues to sin and must continually repent of that sin. Furthermore, Sin brings Punishments.  This is a concept that is clearly displayed in the Scriptures. It is essential for a Catholics to maintain there relationship, this is done through the Grace of the sacraments.

It may seem that I'm going off track a little.  I hope to bring it all back into focus at the end.

After a Christian is initiated into the Church through Baptism Eucharist and Confirmation, they are to use the sacrament of Reconciliation to remove the Guilt of sin, and perform Penance in order to repair the damages to their soul caused by sin, and to make reparations to damages caused to others. The Priest will give the confessed sinner, some manor of reparation, either prayer, Charity or fasting, or some other means by which a person repairs the damage they have done to themselves and to others.  If a sinner who commits a mortal sin, and has a valid confession, the guilt of sin is removed from the soul.  If the Penance is not done, the damage caused by the sin will need be repaired in the afterlife by means of purgation. 

The Sacrament of Reconciliation is not only efficacious, but a preparation for the day of judgement when the soul must answer for all that they have done.  Practice if you will, Humility training for when you stand before the lord.  So like Adam, when God meets you in the Garden and asks "Where are you?" you will have the answer ready on the tip of your tongue


  My God, I am sorry for my sins with all my heart.
  In choosing to do wrong and failing to do good,
  I have sinned against You whom I should love above all.


The Devil, whose tricks do not change, preys on the weak, and none are weaker than those who are suffering and dying. It is for this reason that the Church has the Sacrament of "the anointing of the sick" which includes the Viaticum, the food for the Journey, the bread of life which is Christ, which also has the power on its own to forgive venial sins. A Christian who asks for the Extreme unction is still not out of hot water, the mind weakens from suffering can still be led astray, temptation to end ones life by means of Doctor Assisted suicide is a danger for the suffering.  This is why Catholics pray, some daily for the intercession of the Virgin mother. 


  Hail Mary, full of grace. The Lord is with thee.
  Blessed art thou amongst women,
  and blessed is the fruit of thy womb, Jesus.
  Holy Mary, Mother of God,
  pray for us sinners,
  now and at the hour of our death. Amen.


See this link for a discretion of the Rosary in Sacred Scripture

Especially at the hour of death, this prayer to Jesus, honoring his mother.


  Luke 2:35 "...and you yourself a sword will pierce so that the thoughts of many hearts may be revealed."  


Faced with the prospects of all eternity in the presence of the One True God, or that of damnation, the Catholic who practices his faith does so with the intention of succeeding in the one and only purpose for our creation.  The Conscious act of which the Lenten Missal addresses is the state of your conscious at the time of death.  Are you concerned with the agony of your flesh or the dispensation of your soul in your last moments.  Will you curse God for your agony or unite yourself to the sufferings of Christ on the Cross.  Will you, in order to relieve yourself of the pain, or the financial burden on your assets which you intend for your children, choose to end your life before its time? Would you under duress, deny Christ?  The Sacraments, the liturgy, the Prayers of the Church, Prepare our conscious for that time and the difficult thoughts and decisions and actions that we must face.

The conscious act is your perseverance to the end, through trials and tribulations, sometimes pain and discomfort. A prepared soul, who has prayed their entire life for the strength to persevere, and given the Grace to do so though the Sacraments of the Church, the intercession to the body of Christ, will have a conscious that acts according to the sacramental prayerful life they lived. Even the mind which seems to sleep will dream of the Scriptures or contemplate the mystery of salvation.

Compare this to a person who simply states that they have absolute assurance of their salvation, the sin of Pride and presumptions, an echo of the fall. 


  where are you?