There are Demons (spirits) and fallen angels along with satan who will be with those in Hell making eternity just plain hell!
Demons are spirits that came from the dead Nephilim who were the giants in the Old Testament (Genesis 6) certain fallen angels that mated with human woman and had well giants. They were killed (but not all) in the flood and those spirits that came out of the nephilim are still with us today. looking for a body to go into as human bodies were all they ever knew hence alot of this past life stuff is demons, of course they can put false memories inside a person, they were there.
The certain fallen angels that were guilty of this are now locked up in chains (Jude)