My general advice, no matter the kind of event, is to make sure you have some sort of safe space - some sort of closed-off space you can retreat to when things get too much. If there's nothing else, then a bathroom with a locked door is always an option. Make sure to find this place as soon as possible after arriving, so you know where it is.
Then, come prepared with things that might help you in a small bag. Headphones, earplugs, fidget toy, book, food, drink, phone, anything that might make things easier for you. You'll at least be able to use them in your safe space, if nowhere else.
Plan regular breaks where you retreat for a short while. Bathroom breaks are generally accepted, but also (fake) smoking breaks, or "I just need some air for a second". For a longer break, it can be good to plan a scenario beforehand ("I have to make an important phone call around xy o'clock, so I will be gone for about 15 minutes then").
Related: A fellow ND friend and I have the habit of letting each other know when we have social duties but our batteries are low, so in an emergency, one can send the other a very short text, and the other one calls with a fake emergency that gives you an excuse to step away for a bit.
During those breaks, you can do whatever helps you to recover a bit. Listen to music, put on noise-cancellation, do some short meditation, have a cry, whatever helps.
I get totally dizzy around people especially when closed in, and will no doubt say something dumb or run into a door.
Make sure you drink enough water and eat enough. That way, at least physical reasons to get dizzy will be lower.
Also, have an emergency exit plan ready to use if you really need to leave.