First off, I don't like the term "lose your salvation." This to me implies that one day it was there and the next day it was gone with no explanation whatsoever of how it got lost. I don't believe people "lose" their salvation. However, I do believe people can "walk away from," "give back," or even "drift from" salvation, and I believe the Bible states that such can happen.
If I were to stop right here a huge question should be forming in the minds of those reading. Just how does this happen, and if it does happen how does a person know it hasn't happened to them? Such an idea, if not fully explained, can cause a person to doubt their salvation. Clearly salvation is a free gift and cannot be earned. That is what Scripture reveals, but when a person hears that it possible to be saved at one point and not at another it often produces the effect of immediately looking to one's works for the answer. "Am I doing enough to keep my salvation?"
Works are not what is in question here. A person does not gain or lose salvation by what they do. If it can't be acquired through works how can it be "lost" through works as well? Salvation is obtained through belief. Belief influences behavior. Behavior confirms salvation, but each person is in a process of completion meaning that every person is at some different level of faith and obedience.
Both the letters to the Galatians and Hebrews indicate that salvation can be "abandoned" or "drifted away from." Look at the following verses.
"I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel..." (Gal 1:6)
"Therefore we must pay much closer attention to what we have heard, lest we drift away from it." (Hebrews 2)
Now one might make the argument based on observation that neither of these verses expressly say that it is salvation that is being abandoned (deserted) or drifted away from, but it cannot be denied that the authors of these two epistles were writing to two groups of people who were turning their backs on the message that brought about salvation. A message they once accepted as true! The obvious indication is if one turned their back on the Gospel message, or in the case of the book of Hebrews the teaching of who Jesus Christ is (which the Gospel hinges on), they turn their backs on salvation.
This is where we come to an understanding what it means to abandon or drift away from salvation. What saves us? Faith! Faith in what? In the Gospel message (Jesus Christ). How can a person continue to be saved if they quit believing in the Gospel revealed through Jesus? A person "loses" their salvation when they once accepted and then reject the Gospel message.
So if you are a believer struggling with sin don't question your salvation. Question who is in control of your life at the present moment. You can't earn salvation, but you can live it out through obedience to Jesus. So I am not giving anyone an excuse to not live out their salvation, but I am saying that even if you struggle in some area of sin it does not mean you are not saved. It simply means you are human and in continued need of the daily saving grace of Jesus our Savior.
On the other hand, know the Gospel message. Embrace it. Stake your life on it. Share it. Above all, don't abandon it or drift from it by listening to teaching that clearly contradicts it. There is only one way to be saved, and it is through faith in Jesus Christ. He is the only one who is uniquely qualified to save mankind being one complete person with both the divine and human nature. Only he can fulfill the requirements of the law and give us hope for the future.