Some people think that getting “saved” isn’t really any deeper than an individual responding to an altar call, or being baptized and joining a church, or showing some other outward sign of religious behavior.  Some think of it as simply a “feeling”. 

However, it is far more than that.   When an individual makes Jesus Christ their Lord and Savior, and are counted among the redeemed by God, their spirit is regenerated, they are seen as forgiven, perfect, and sinless in God’s sight.  They are adopted into God’s family and raised to the status of a co-heir with Christ.  We are then given God’s spirit as an earnest or guarantee of our coming glorification

With that in mind, lets play out an scenario.  John B. Christian makes a commitment to Christ when he is a teenager.  God affects all of the benefits mentioned above.   He falls away for a few years, but then recommits himself in his twenties.  Do we imagine that he became “unsaved” for those wayward years, was removed from God’s family, returned to his state of being unregenerate, and then later, when he recommitted, had all of that reversed again? 

Not very likely.  Such as the story of the prodigal son, one can be a son or daughter of God, and squander their inheritance, but still be in the family of God.  God still loves them, still rejoices in seeing them, still longs to be with them.  God’s grace and mercy is unfathomable.   

Part of the problem in this debate is that individuals look at salvation just from the manward side- that is, viewing salvation in terms of our behavior, or profession.  However, when you see the “Godward” side, that all of the aspects of what God accomplishes in us when we are saved, then you realize that one cannot simply become “unsaved” and then “resaved” again.  That, I believe, is the gist of Hebrews 6:4-6:

”For in the case of those who have once been enlightened and have tasted of the heavenly gift and have been partakers of the Holy Spirit, and having tasted of the good word of God and the powers of the age to come, and then have fallen away, it is impossible to renew them again to repentance, since they again crucify to themselves the Son of God, and put Him to open shame."
(Hebrews 6:4-6.)

One does not simply become saved, then unsaved, and then saved again.  Some see the verse above, and see only how by backsliding, one can never be saved again.   However, in light of the fact that the whole context of the book is arguing for the permanency and security of the New Covenant, isn’t it more likely that the thought is that one isn’t saved-unsaved-resaved again?  In context, the author is arguing against seeing salvation as a state that one can casually slip in and out of. 

Although there are a tremendous number of verses that speak of the Security of the Believer in Christ, there is a fairly definitive verse in 2 Timothy 2:12-13.  It seems to me to express the very balanced position that a Christian cannot, simply by a weak faith, become unsaved.   You can, however, repudiate Christ and be lost.  It says:

 'If we endure, we shall also reign with Him. If we deny Him, He also will deny us. If we are faithless, He remains faithful; He cannot deny Himself.”

I would venture the speculation that there are many individuals who feel lost, may appear lost, and would deem themselves as “faithless”.  However, there was a point in their lives that God regenerated them through his Holy Spirit, and thus he will never deny them.   Many of those people may never go back to having a vibrant relationship with God during their lifetimes, simply because they think that God is fed up with them, and is interested in bring them back into the fold.   However, from God’s perspective, they are still seen as having the righteousness of Jesus, and are still just as much “family” as they ever were. 

So the short answer to the questions is:"No, you can't "lose" your salvation, as if it simply slipped away from you, or by faithlessness, or inattention it just got away.  God's keeping power is greater than we imagine.