Curse of Nightmare

You sit and focus on a creature while holding item that belonged to that creature. That creature must be asleep or unconscious for this spell to succeed. 

When the spell is completed you describe a nightmare for the creature you focused on to have. You can provide the basic guidelines of the nightmare (eg: Being chased, feeling overwhelmed, losing a fight to a monster etc. ). If the creature makes a Wisdom Saving Throw against your spell save DC. On a failed save the creature suffers the nightmare you described. If ritual is used on same creature 3 days in row it  is unable to sleep properly and becomes cursed. Creature can regain only half of it's spell slots round down and have disadvantage on wisdom saving throws until they complete a Long Rest.