Excuses after not showing-up at the meeting:
Family Emergency
Sudden Migraine
Nosebleed
Ate something that didn't agree with you
Long phone call and time got away
Household emergency (ie: broken water pipe)
You were exhausted and fell asleep when you sat down for 5 minutes after dinner
You had forgotten you were assigned a talk.
or how about the truth?: I didn't feel up to giving the talk/attending the meeting. You could let him know in advance to have someone else give the talk. Whether he likes it or not should not be your concern.
You would benefit from changing your thought process. Best not to use the words 'weasel out' or other derogitory terms about yourself.
Although you are likely responsible, conscientious and reliable, sometimes you need to place your needs first. The fact is, your body is telling you not to do something, pay attention! This is not a weakness but maybe for your own good.
Even though you may have committed to doing something for someone else, what good are you to anyone if you don't take-care of your own needs and become worn-out and incompacitated as a result.
You are an adult and can make your own decisions whether anyone else likes it or not. No excuses are really required.