|"Is this all real? Or has this been happening inside my head?"
The topic of this article is of a real-life subject that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really existed), and, as such, details contained in this article may differ from real world facts.
Chestnut (genus Castanea), some species called chinkapin or chinquapin, is a genus of eight or nine species of deciduous trees and shrubs in the beech family Fagaceae.
According to Garrick Ollivander, this was a most curious, multi-faceted wood, which varied greatly in its character depending on the wand core, and took a great deal of colour from the personality that possessed it. The wand of chestnut was attracted to witches and wizards who were skilled tamers of magical beasts, those who possessed great gifts in Herbology, and those who were natural fliers.
However, when paired with dragon heartstring, it might find their best match among those who were overfond of luxury and material things, and less scrupulous than they should be about how they were obtained. Conversely, three successive heads of the Wizengamot had possessed chestnut and unicorn wands, for this combination showed a predilection for those concerned with all manner of justice.