Dear Sarah,
I was so incredibly sorry to miss your birthday bash last Saturday. I had been looking forward to celebrating with you for weeks, and I feel terrible about being a no-show.
Unfortunately, I came down with a sudden and quite severe bout of food poisoning on Friday night. I spent the entire weekend confined to my bed, feeling absolutely wretched and unable to even stand up, let alone travel across town to the restaurant. It was honestly one of the worst experiences I have had in a long time, and I am only just starting to feel like a human being again today.
Please accept my sincerest apologies for letting you down at the last minute. I know how much effort you put into organising the evening, and I truly regret not being there to share in the fun.
I would love to make it up to you as soon as I am back on my feet. Are you free next weekend for a belated birthday lunch? My treat, of course!
Best wishes,
Mark