Go get it checked out as soon as possible and then you will know what the damage is and the doctor may give you some stronger painkillers.
Surely your friends will understand, you are not letting them down on purpose.
Let me know how you get on.
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Pegasus
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“Everybody is a genius. But if you judge a fish by it's ability to climb a tree, it will live it's whole life believing that it is stupid.” - Albert Einstein