First of all, it is okay to say No to a party simply because you don’t want to go.
If it is a host you are not that close to, you can always say things like: Sorry I already have a prior commitment that day and I cannot cancel it.
Now, if you decide to go, wear comfortable clothes. If it is a party with theme or dress code, wear the comfortable version of that dress code if such a thing exists.
Before you leave, lay out your “returned home” clothes , makeup remover etc. so you can change into something comforting and get ready for bed immediately.
What you can pack for the party:
energy bar or snack if you have sensory difficulty with food textures,
noise cancelling headphones,
earplugs or noise cancelling earphones,
You are at the party now
Try to be the first ones to arrive if you can. You can choose a spot you like and gradually get used to people flowing in.
Grab a glass of water or drink and hold on to it. People will automatically assume you are drinking and having “fun”.
If you have sensory difficulty with food texture, eat before you go to the party. Have a plate with something and people will think you have been eating. Keep a small packet of energy bar or small snacks in your bag in case you really get hungry again.
It is okay to shut down once in a while.
If it is your birthday and you do not want people to sing, tell them. It is your day and they should listen to you.
If you have a close friend or partner in the party, have a code word or gesture that will inform them that you are in distress or overwhelmed.
If you feel overwhelmed, try to find a quiet corner. If there is no quiet corner, offer to quickly step out and get something (ice, cigarette, wine). Walk around the block for a bit before you return.
If you still feel overwhelmed and want to leave, do so.
Set yourself a deadline of when you want to return home. Leave at that time. Acceptable excuses to leave early include:
I have an early day tomorrow.
I have a headache.
I forgot my medicines and I need to take them now.
I started my period just now and I should head home soon.
My housemate/neighbour/pet sitter called and my pet is not feeling well.
Unwind from the party
Once you are back home, change into comfortable clothes.
Take a shower if you have energy.
Listen to nice soothing music/ podcast/ audiobook.