Q. (1) If God has forgiven my sins, why will I be judged again? (2) During death we are “sleeping.” So where do ghosts and spirits come from?
(1) Regarding your first question, please see this post:
(2) Regarding your second question, I should acknowledge first that I do not share your understanding of death as “sleep.” I have another post on this blog entitled, Do the souls of believers “sleep” after death until the resurrection? In that post I say that “my overall sense from the Bible is that the soul of a believer does pass directly and consciously into the presence of God upon death.” Correspondingly, a person who has not chosen to believe would pass directly into a situation of separation from God.
Accordingly I do not share the further idea, which you seem to question yourself, that “ghosts” are the spirits, still going about on this earth, of people who have died. I do not see any support for that idea in the Bible. So maybe one good way to put this is, “There’s no such thing as ghosts.”
As for spirits, however, the Bible does indicate that in addition to making visible creatures with physical bodies, God also made invisible creatures that exist in the spiritual realm. That is where spirits come from. The Bible teaches further that some spirits have chosen to remain loyally in God’s service, while others have rebelled and now oppose God. These would be angels and demons, respectively.
That is why John writes in his first letter, speaking specifically of how a spirit would inspire a prophet to say something, “Do not believe every spirit, but test the spirits to see whether they are from God.” We might say more generally, “Do not trust every spirit that you think may be having an influence around you, but make sure that you only welcome the influence of spirits that are genuinely still in God’s service.”
But I would conclude with this caution. By and large people are not aware of spirits and their influence. Most people do not have the capacity to discern their presence and activity. So I think it is best for us to concentrate on what we can know with a reasonable degree of reliability, such as the way of life that God teaches us in the Bible to follow, and leave the workings of the unseen world to God. As a wise older Christian told me when I was a teenager, “Don’t see a demon under every couch.”