In school I never said much, too busy having a headrush
A headrush is a slang term for vertigo. It describes that sensation when you stand up too fast and feel light headed and dizzy. But a headrush can also be induced by drug use, which is most likely what Em is talking about here.
To help improve the meaning of these lyrics, visit “Just Don't Give a Fuck” by Eminem Lyrics and leave a comment on the lyrics box