How do I handle the stress of big high-visibility events?

You can coordinate events now, and the big, high-visibility ones still push you past your limit. That is not a sign you cannot handle them. High-stakes events carry more moving parts and more eyes, and the pressure rises for everyone who runs them, including the seasoned. The stress is proportional to what is at stake, not to your ability. Much of what overwhelms you in a big event is trying to hold it all in your head at once. The people who stay calm at scale do not have bigger memories; they externalize everything, into checklists, timelines, and clear owners for each piece, so their mind is free to handle what comes up live. For your next big one, get the whole thing out of your head and onto a detailed run-of-show, and hand specific parts to specific people so you are not the single point holding it all. Your job on the day becomes steering, not carrying. Scale gets survivable when you stop trying to hold it alone.