Can we lose our salvation once we've accepted Christ?
The short answer is yes. It isn't an isolated occurrence. It has been happening with increasing frequency as Christians listen to those of the world who say there is no God. It's warned about in the Bible over and over. And some verses speak of the great thing it is to bring someone back to Christ who has turned away.
Rather than repeat all the scriptures here, I'll refer you to another page I've prepared that was written by Finis Jennings Dake and included in his Annotated Reference Bible. It has 210 verses, organized by writer, covering the Old and New Testaments. Keep in mind that the writings of the apostles were to Christian churches they had established and Christian ministers who were trying to start and shepherd other churches. The verses Dake has listed in 210 Plain Laws and Warnings were written to believers. If they had to worry about keeping true to the end of their own lives, we have no less a commandment.
I know that 210 verses seems like a lot. But it is worth reading through the list anyway. Even if you just take one author like Paul or Peter from the New Testament and read their verses, know that they were telling you what God expected of His people. For this topic, number 48, 51, 88, 152, 158, 163, 165, 197, and 201 are particularly good. God hasn't changed. Stay true to the end and reject the deceitfulness of the enemy of your souls.