From among the punishments of sinful acts are that they cause the servant to forget himself..

When a person forgets his soul, he corrupts it, and then destroys it.  If o­ne would ask, “How does someone forget himself if he does forget?  Which things does he remember?” Allaah سُبحانه وتعالى has said,

وَلَا تَكُونُوا كَالَّذِينَ نَسُوا اللَّهَ فَأَنسَاهُمْ أَنفُسَهُمْ أُوْلَئِكَ هُمُ الْفَاسِقُونَ

"And do not be like those who forgot Allaah (i.e. became disobedient to Allaah) and He caused them to forget their own selves.”

[Suratul-Hashr 59:19]

In other words, Glory is to Him, Allaah سُبحانه وتعالى punishes the o­ne who forgets Him with two punishments:

(1). Allaah سُبحانه وتعالى forgets him.

(2). He سُبحانه وتعالى causes the individual to forget himself. 

Allaah’s forgetting the servant involves His disregard, abandonment and neglect of the disobedient o­ne. As a result, destruction draws closer to him than his own face and hand. 

As for the sinner, his forgetting himself means that the person stops thinking about the finer qualities of the soul and the things that lead to its success and well-being.  He forgets all of this.  The matter does not even come to mind.  Nor does he bring it to mind.

In addition, the disobedient servant is made to forget the diseases of the heart and soul along with the agony that accompanies them.  In the end, there is no effort to remove these destructive ills that of which eventually lead him to corruption and ruin. He becomes a sick individual covered with layers of disease. The internal disorder causes destruction to spread through him.  However, this negligent soul is not aware of his sickness nor does the remedy occur in his mind. 

This is the worst kind of punishment. What punishment is worse than an individual neglecting, and then destroying himself? He forgets the beneficial qualities his soul possesses.  This rebellious servant becomes heedless of the causes of his acquiring good in this life and a permanent resting place in the abode of eternal bliss.

{'Sins & their Punishments' by Ibnul Qayyim al Jawziyyah رحمه الله Pages: 54–56}