Psalm 32

"When I kept silent, my bones grew old through my groaning all the day long.
4 For day and night Your hand was heavy upon me; my vitality was turned into the drought of summer. Selah
5 I acknowledged my sin to You, and my iniquity I have not hidden.  I said, “I will confess my transgressions to the Lord,”  And You forgave the iniquity of my sinSelah" 
vv.3-5

Read chapter 32.
Here we have David talking about unconfessed sin.  When kept silent about it, not just to other people but to the Lord too, it eats away at the body.  The guilt that is felt in our minds effects our bodies, depriving us of sleep, causing stress to the bones, maybe even gray hair, depression and multiple other ways for every individual. David is possibly thinking of a specific occasion in his life here of his sin with Bathsheba and killing her husband Uriah.  David doesn't confess this sin for around a whole year as we know it didn't happen till after the baby was born (read 2 Samuel 11 & 12 if you're unfamiliar with that story).  
When David was called out by the prophet Nathan of his sin, he admitted and repented and God forgave him.  Today we do not need to confess our sins to be forgiven as we are already forgiven all our sins by Christ's death.  We can and should confess our sins to God to give Him the weight, guilt and shame we put on ourselves, but we must not think that confession is what secures us of forgiveness.  Christ has already done the work to forgive us all our sins.  All this seems to be for the believer and not the unbeliever (although unbelievers too can carry guilt shame but for other reasons than Christ's way).
What sins are you keeping silent about that cause you guilt and affecting your daily life or body?