You don’t dream normally anymore. Instead, you take a look into an alternate reality where you ended up with something you wanted right now, in such way that would make you feel sad.

For example, if you had recently lost a loved one, you could dream about them still being alive, or maybe you had just gotten rejected by the person you liked, and you would see what would’ve happened had they chose to be with you.

The sadness would make you somewhat close to tears, but not exactly. It’s sadness in a way that you can still hold back crying. If you are simply content and don’t really have anything to be sad about, or have an extreme tolerance to sadness, the ability can literally just conjure entire stories to make you sad.

Lastly, if you truly could not, in any way, feel sadnessz then this power just doesn’t work.