Calvin: sorrow

Repentance will produce confusion, groaning, displeasure with self, but...

...we must remember to exercise restraint, lest sorrow engulf us. For nothing more readily happens to fearful consciences than falling into despair. And also by this strategem, whomever Satan sees overwhelmed by the fear of God he more and more submerges in that deep whirlpool of sorrow that they may never rise again. That fear cannot, indeed, be too great which ends in humility, and does not depart from the hope of pardon. Nevertheless, in accordance with the apostle's injunction the sinner always ought to beware lest, while he worries himself into dissatisfaction weighed down by excessive fear, he become faint.

Institutes , 3.3.15 (Battles p.608-9)

Which also I think fits well with a great passage in 1 Samuel 12:

And all the people said to Samuel, “Pray for your servants to the Lord your God, that we may not die, for we have added to all our sins this evil, to ask for ourselves a king.” And Samuel said to the people, “Do not be afraid; you have done all this evil. Yet do not turn aside from following the Lord, but serve the Lord with all your heart. And do not turn aside after empty things that cannot profit or deliver, for they are empty. For the Lord will not forsake his people, for his great name's sake, because it has pleased the Lord to make you a people for himself.

Repentance

It is important to consider how the gospel affects and transforms the act of repentance. In 'religion' the purpose of repentance is basically to keep God happy so he will continue to bless you and answer your prayers. This means that 'religious repentance' is a) selfish, b) self-righteous, c) bitter all the way to the bottom. But in the gospel the purpose of repentance is to repeatedly tap into the joy of our union with Christ in order to weaken our need to do anything contrary to God's heart.

Tim Keller, All of Life is Repentance