Does the SDA demonination believe that you can lose your salvation?
This is quite a challenging question. I'd say, "No, you cannot lose your salvation unless you decide to do that yourself!"
The greatest decision you make in your life is to let God himself through Jesus Christ, the WORD, and the Holy Spirit be the supreme Guide in your life. This is a challenging life that leads to eternal lilfe in Christ, and without Him there is no eternal life. Scripture makes it clear that only God is immortal. No other being in the universe is immortal, not even the angels, because some of them decided to follow Satan and become the tempting demons around us.
When even an angel can fall (Rev. 12 tells you that one third of the angels followed Satan, but thank God that there are two good angels to our rescue for every evil angel that attacks us) - when it is possible for them to fall, then it is also possible for man to fall.
So if a man gets tempted by a demon to be bad he cannot fall as long as he keeps a living connection with God. If he lets go - that is where the danger lies.
There is a way out: 1 John 1:9
9If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.
Our way back goes through forgiveness. But
8If we claim to be without sin, we deceive ourselves and the truth is not in us. 9If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. 10If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives.
So if we hide our sins and act as if we never sinned, then there is no chance to be saved.
Some think that it is often very difficult for the most conservative Christians to confess their sins. They'd rather hide them in order to make the appearance of being perfect.