I dreamed of meeting someone in the underworld to celebrate my birthday, okay?

Don't think too much, there is nothing wrong with this.

The so-called daydreaming dreams at night. People in this underworld usually have birthdays recently or already, and your participation impressed you deeply. At the same time, you will also think of people who have passed away. So dreaming about this situation can't predict anything. So don't think too much about normality.