Feeling Drained and Anxious About Social Plans

Okay i’m feeling drained. My period started yesterday, my allergies are at an all time high (because spring). I over exerted myself yesterday. i was out doing social shit from 11am-midnight. now i want to back out of plans that i was originally just kind of added on to. like two friends were going out and i was invited to join them. I really like these people and i want to keep them as friends but i know i’m not going to have a good time. it’s going to make my anxiety worse. I kind of want to force myself to go because what if i do have fun? but I literally have less than five hours before i’m supposed to leave and i don’t want to wait any longer than i have to to cancel but i’m still not sure if i want to cancel. definitely FOMO. I also have work tonight. how do i cancel and keep friends. (sorry the post is so long)