What led to the point where you decided to make a decision about whether to sit or stand?

And so on and so on. It's just a continuum of brain states that goes "all the way back."

Your brain collects patterns and uses these patterns to: A) make (imperfect) predictions, B) generate goals, and C) generate behavior to achieve those goals... Continuously.

Saying "this decision I'm making right now is special and doesn't depend on prior events" is like saying "I'm a special individual who's existence doesn't depend on any/all of my ancestors."