I was sick with anxiety about my son's wedding for at least a year before it took place. The fear was a million times worse than the event.
I was extremely worried about seeing my exes family plus I'm a recovering (sober) alcoholic so I was terrified of drinking due to stress and ruining the whole thing.
I didn't sleep properly for a year before but once I was there I just handled it. I probably trained myself with Tara Brach & Eckhart Tolle podcasts etc etc for that whole year leading up to it. All I can say is that my imagination had it a million times worse than the reality.
I have social phobia anyway but big family events are the worst scariest thing ever!
Sometimes before an event I'll take loperamide to calm my nervous colon and valerian for my nerves. Tapping helps me as well.
You're not alone, it's really incredibly stressful is you're a sensitive person. What really makes me laugh is that most people didn't even recognise me because I wasn't important to their reality at all, I no longer even existed for them.