Excuses for missing school.?

okay so ya todays halloween, and im feeling sick. i've been sick on halloween for the past 4 years. (it has something to do with the weather changing or someting im not too sure) so ... i missed the morning of school and my mom said that i could go to this hall. party as long as i go in the afternoon. well ... im still fealing sick and i know im going to have to miss the afternoon, but i REALLY want to go to this party. so, im not going to tell my mom (whos at work, both parents are at work im home alone) that im missing school this afternoon and im going to lie and say that i went. but, my friends will all know that missed cuzz some of them are in my homeroom. so, what can i tell my friends the reason why i missed school. they will think that im faking if i say that i was sick (cuzz their going to the hall. party too) and i need to tell them something like for example: oh i had to go to this ____ and then in the afternoon i had ____. and dont say appointments cuz i had one yesterday.