If you are not a true Christian, then the instant you die, you go into the equivalent of a dreamless sleep.
The penalty for sin that was given to Father Adam was death. Genesis 2:17 “But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.” Please remember that a day with the LORD is as a thousand years (2 Peter 3:8). Adam died at 930 years of age (Genesis 5:5) which is within a day (according to the LORD).
We are under the same death penalty as Adam. So does the Bible tell us death is like? Yes! A description of the death condition is found in Ecclesiastes 9:10 “Whatsoever thy hand findeth to do, do it with thy might; for there is no work, nor device, nor knowledge, nor wisdom, in the grave, whither thou goest.”
This describes a dreamless sleep. There is no thought or conscience when you are dead as further described in Ecclesiastes 9:5 “For the living know that they shall die: but the dead know not any thing…”
Even Jesus described death as sleep. His disciples were confused when Jesus told them that Lazarus was just resting. John 11:11-14, “…Our friend Lazarus sleepeth; but I go, that I may awake him out of sleep. Then said his disciples, Lord, if he sleep, he shall do well. Howbeit Jesus spake of his death: but they thought that he had spoken of taking of rest in sleep. Then said Jesus unto them plainly, Lazarus is dead.”
These scriptures describe the death condition as a sleep condition. All mankind who experience death will eventually be awaken from this death/sleep condition in the future resurrection. (John 5:28, 29)
However, the instant a faithful Christian dies, he is instantly changed into a divine, heavenly being. 1 Corinthians 15:52-53, “Behold, I shew you a mystery; We shall not all sleep, but we (Christians) shall all be changed, In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.
For this corruptible must put on incorruption, and this mortal must put on immortality.” (See also 1 John 3:2)