I tihnk the question that needs to be asked here is 'did you learn from this?' and 'Would you disobey again?' If the answers to these are no and yes then the punishment has failed.

What you maybe should have learnt from this is to ask permission before taking any kind of break from set tasks. It is easy enough to send a mail saying 'Please, Master, may I take a day of rest...' maybe listing reasons why you feel you need it. He may say no but he is more likely to say yes (unless you have given him reason not to such as recent disobedience in other tasks) and, more importantly, you get the day off without any repurcussions.

No sub should be in a position where they feel that they cannot ask a Dom/me for permission to change the rules or ignore the rules for a time or something like that.