Overthinking is memorizing lines for a play nobody is putting on.

Rehearsing conversations feels like preparation, which is why it is so hard to stop, and the version you are preparing for almost never happens. Real exchanges go somewhere else within a sentence, and all the scripting leaves you with is a tired mind and a stiffer delivery. The energy goes into a performance nobody scheduled.

Notice when you are drafting a scene rather than actually thinking. Decide the one thing you want to say and let the rest be improvised. If a conversation needs to happen, having it is usually quicker than a week of rehearsals.