The Psychosomatic Curse

You curse a creature you can touch with mania. The creature must make a Wisdom saving throw or undergo a hallucinogenic affect. The cursed creature becomes plagued by one of their phobias, and becomes irrationally convinced that said phobia is physically changing their body. (Example: A creature afraid of insects may hallucinate bugs under their skin.) The creature becomes anxious and afraid, gaining the frightened. Whenever the creature attempts to explain its condition to a willing creature, it must make a Charisma saving throw or lose its tongue to mad ramblings. 

The creature may attempt to harm itself in order to remove the source of the phobia. (Example: Scratching incessantly at the skin to get rid of the aforementioned bugs.) During combat, it will spend its movement actions attempting to get away from the source of the phobia, and will either spend its actions on the Dash action (if possible) or attempting to attack the source of the phobia (if possible), which can lead to them accidentally harming themselves. It is up to the DM's discretion whether or not they do harm themselves, and for how much damage.

ENCHANTMENT/CURSE SPECIFIC:

This spell can be infused into non-magical items to make them magical. Items such as rings and necklaces when worn cause you to go under the effects of the spell without the wearer's knowledge. However, they are allowed to make Wisdom saving throws every hour under the effect to identify the source of the effect (the cursed item). When imbued into an item that can't be worn, it has to be making physical contact in order to trigger the effects of the spell. When placed in clothes that are being worn, it counts as touch. The effects of such an item are effectively the same as the above description. Additionally, the longer the creature is cursed, the worse the effects become.