Curse of "The Follower"

The Nature of the Curse: A curse passed down through generations of the Rhodorim family as a near breakable curse. The curse torments the victim with unending nightmares about being followed with no visible person behind them. There is only one way to break the curse and that is to gather all of the 3 Feathers of Solitude and a powerful mage familiar with the curse must combine them with the blood of the curse's target to free them.
The curse is placed on another using the last life force that the caster has to place all of the malice and spite they have into the person's soul
The Curse Itself: The afflicted person will suffer from nightly nightmares that change in severity the longer the afflicted is subjected to the nightmares and depending on their mental fortitude. In the real world, a misty creature would lay/be on top of the sleeping person. None of the weapons, items, or anything come into the dream with the affected person. The sleeping person will react similarly to how they do in the dream but to an extent. They will toss and turn instead of actually running and will flail around in place if they are fighting but will not actively use a weapon even if it was in their hand as they fell asleep.
The affected cannot be woken up by force from reality. There are only two ways for the affected person to be awoken from their dream: Either the beast/misty figure must be shot/hit enough to reduce the HP of it to 0 or the beast must kill the affected in the dream. Once the figure is shot/hit, the affected person is able to wake up. However, if the beast kills the affected in the dream, they will fall into death saves and be on the brink of death upon "awaking" from their dream. Unless a team member can save them or they can successfully stabilize themselves.
How the Curse Activates (Gameplay Specific): Once the curse is placed, every time that the affected goes to sleep (either long or short rest; unconsciousness does not apply), they must roll a Wisdom saving throw.  There is no firm guidance on what the DC must be for the affected to not have a nightmare.  However, each time the affected does have a nightmare, the DC does increase.  The first time the curse is activated the DC was a DC 10 and it was only a minor nightmare.  Each nightmare following became more and more aggressive depending on how severely the Wisdom save was failed or if it was only marginally surpassed.
If the party stayed up to watch the nightmare, they were able to see nothing but the affected tossing and turning/having a nightmare until the curse became more severe and the curse chose to reveal itself to them.  Otherwise the team must use "See Invisible Objects" or a similar spell to see the creature.  Depending on their perception, they can see either the misty shape of the creature or the full creature.  The creature also progressively gets larger and more defined as the curse takes effect more times.

Known Casters: Irnashtid Rhodorim
Cast During: The Missing Daughter

Some examples of the curse's impact from least to most severe:

1. Walking through an endless white void when you feel a tap on the shoulder. When you turn around, there is nobody there.
2. Walking through a seemingly endless field with a blue sky above. As you walk, you feel something grab and tug on your arm and when you turn around, nothing is there.
3. As you walk through the endless field from before, but can feel a large presence behind you. When you run away from it, you hear a loud and heavy footsteps getting closer and closer to you until you feel the weight crush you from behind and keep you pinned to the floor.
4. You are attacked by a 3 headed Chimera with heads of an eagle (griffin), lion, and a third head that looks like a blob on default but the exact form changes each time that you look at it or blink. The beast also can show itself in the real world as well if it so pleases the beast. Otherwise, it will still show itself as a misty creature in the general shape of this Chimera.