In my understanding of scriptures, there is one death for some, and two deaths for others. In the first death, which all or certainly most all experience, we lose consciousness. We know nothing, not even that we are dead. We can no longer Sin, nor can we praise God. But our individual spirit is persevered by God for a resurrection in which we will become conscious again and judged by the things we have done. In the realm of time, that God created, this would be in some cases centuries, as with Noah. But because God, nor the spirits that return to Him, are not influenced by time, when the dead are raised, it will seem like only seconds to them. Like the Rich man in the Parable Jesus told had no idea that he had been dead for 1000 years while Abraham and Lazarus reigned with Christ. I can post the Scriptures for anyone who wants to see them. For some, this resurrection is permanent, as the Judgment they receive, isn't eternal death but eternal life. But for others, the judgment is another death. This death, called the 2nd death, is everlasting. It is a death from which there is no return, in which we do "cease to exist completely".
It is a fascinating subject, and according to scriptures, is pretty simple to understand. However, because men don't really believe much of what is written, and no one wants to die, there have been myths and religious tradition, and even huge businesses created around the topic of death since the very beginning, when the deceiver convinced Eve, "Thou shall surely not die". Certainly, a popular religious philosophy in this world that God placed us in.
Great topic.