You might be wondering how this could happen apart from a contrived scenario of casting a spell like cause fear on yourself (which is allowed). Turns out, it can happen by interacting with the local wildlife of Icewind Dale.
The Crag Cat has this ability:
Spell Turning. The cat has advantage on saving throws against any spell that targets only the cat (not an area). If the cat’s saving throw succeeds and the spell is of 7th level or lower, the spell has no effect on the cat and instead targets the caster.
So I cast cause fear on a Crag Cat, it passes the save, and then I fail on my save. I become the target of my own cause fear, which means I am now frightened of myself.
The frightened condition says:
- A frightened creature has disadvantage on ability checks and attack rolls while the source of its fear is within line of sight.
- The creature can't willingly move closer to the source of its fear.
Do either of these conditions apply in some way while I am frightened of myself?
You might be thinking, "why not just drop concentration and end the effect?" Right, that would work, if the caster thought to do that. When this scenario played out in my game, the player whose character was frightened of himself was so worked up about his player being frightened of himself he didn't even think to drop concentration, which I thought was a great narrative expression of the effect. I ruled on the fly that he used all of his movement on his turn to run about wildly, trying to get away from himself, opting to make a quick ruling without spending much time thinking to preserve the tension of the situation. Now that I have had time to think about it, I'm not sure what the correct ruling would be.