I once had a B.F.Skinner type flash (9th grade) when I completely understood all of the arithmetic,algebra,math,trigonometry,calculus after having struggled with those concepts previously. I’ve made my living since exploiting those skills.
Same thing happened with me back in HS. I sucked at math, yet parents were both accountants. Then it just happened, I just called it an epiphany where every math equation looked easy. Add to the mystery was that the HS bullies who beat up other kids for their lunch money were math geniuses..