There is actually debate over doctrine as to whether or not you can lose your salvation. Personally, I dont think you can. If you could it wouldnt be guaranteed. "“Jesus answered them, ‘I told you, and you do not believe. The works that I do in my Father’s name, they bear witness of me. But you do not believe, because you are not of my sheep, as I said to you. My sheep hear my voice, and I know them, and they follow me. And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of my hand.’†We are in a covenant with God, it is based on His ability, not ours. Even though we mess up, He is faithful to keep His word. He will keep you strong to the end, so that you will be blameless on the day of our Lord Jesus Christ. God, who has called you into fellowship with his Son Jesus Christ our Lord, is faithful.
Christians who backslide are also sometimes referred to as carnal Christians. They have accepted Christ but are not trusting in Him, and have reverted to their former ways. Some say these folx dont exist, that you are either a Christian following the ways of God or you never were a Christian and need to become one. I have a problem with the second school of thought, as we wouldnt have been instructed to confess our sins if we were incapable of sinning after becoming a Christian. To my knowledge there is nothing in the bible that says get saved, and then confess any sins as soon as you are aware or you will lose your salvation. You will not be in fellowship with God if you are in sin, but I believe your salvation is secure. Also, as one who has backslidden a time or two or ten thousand, I can tell you that the internal conflict that goes on once you have been saved is nothing like it was before salvation. Things you can do before knowing God you can do with out conscience. Once you are saved, try to do the same mess and see how much peace you get.
Once you are born again, your spirit is recreated and you live under grace, where there is forgiveness for sins, and not pentalties for breaking laws. Sinning does not undo your spiritual rebirth. As a Christian, you have the help of the Holy Spirit dwelling in you, but you still have carnal desires. Renewing your mind in the word feeds your spirit so it dominates your flesh and helps you live righteously.