I believe it's possible for a saved person to turn his back on God and become so distant that he no longer "feels" saved. Salvation isn't a feeling, I realize. Although, the Lord convicts those who are saved...but still allows us to make our own choices.
It's possible to choose to do wrong for whatever reason - and be convicted about it - but the more we sin, the harder our heart becomes and the less we "feel" saved.
I know a pastor who preaches that if you're truly saved, you're not going to sin. If you sin, you're not truly saved. He's named names of those that he's sure won't make it into heaven "he smokes...not saved"..."she is disobedient toward her husband...she's not saved" (and his "disobedience" is my definition of disagreement, which is not a sin). By his standard, the only people going to heaven are those who die immediately upon accepting Christ (assuming they don't cuss on the way out).
People live in the human body, saved or unsaved. All the sins I can think of involves the human body in some way (listening to rock music-the ears...swearing-the mouth...killing-the hands...smoking-the mouth, the lungs....pornography-the eyes) So, let's say a drug addict has hit bottom and is looking for help. He finally meets someone who can show him how he can change his life around and accept the Lord as his Savior. If he does repent and accept Christ, he's still going to want the joint, sniff or puff because his physical body is going to crave it. But the difference this time is he wants to get clean. Unfortunately, he can't just quit drinking if he's been an alcoholic because he could die from it. Quitting a lot of drugs cold turkey will make him sick.
Once clean, it's possible for him to slip up and take a puff or sniff of drugs...but he's still saved.
My parents are saved but they have always had a difficult time getting off the cigarette. Does smoking make them lose their salvation? If it does, I know a LOT of Christians...including pastors...who are not going to go to Heaven when they die. Gluttony is a sin. [shrug] If they die of an illness that is complicated by overeating, then they've pretty much committed suicide, right? Some people believe suicide is the unpardonable sin because they can't ask forgiveness. So, then they aren't going to Heaven, right?
Do you see how easily things can get so twisted around that we can "predict" who makes it to Heaven and who doesn't?
This preacher I know is going to be very surprised when he gets to Heaven (assuming he's saved) and sees who actually makes it to Heaven. Some of the people he's named have told me, "I'm saved, Accepted Christ at **/**/**, I will always be saved, and I don't doubt my salvation one bit". Does this sound like an unsaved person to you?
Naw, Heaven would be very empty if it was possible to lose our salvation. In fact, salvation is the only thing I haven't lost. I lose my keys, my wallet, my comb, pens, important papers (and yet I always seem to come across these things when I'm looking for something else).