Phantasm

You craft an illusion that takes root in the mind of a creature that you can see.

The creature must make an Intelligence saving throw. On a failed save, you create a phantasm perceivable only by the target that is no larger than a 3m-cube for the duration. This spell has no effect on undead or constructs.

The phantasm includes sound, temperature, and other stimuli. The target can use its action to examine the phantasm with an Intelligence (Investigation) check against your spell save DC. If the check succeeds, the target realizes that the phantasm is an illusion, and the spell ends.

While a target is affected by the spell, the target treats the phantasm as if it were real. The target rationalises any illogical outcomes from interacting with the phantasm. For example, a target attempting to walk across a phantasmal bridge that spans a chasm falls once it steps onto the bridge. If the target survives, it still believes that the bridge exists and comes up with some other reason for its fall (e.g. it slipped).

An affected target can even take damage from the phantasm. Each round on your turn, the phantasm can deal 1d6 Psychic damage to the target if it is in the phantasm's area or within 2m of the phantasm, provided that the illusion is of a creature or hazard that could logically deal damage, such as an attacking creature, or burning lava. The target perceives the damage as a type appropriate to the illusion.

It's all in your head.