. . . agreeing to attend a future event and having deep regret you have to do it when the event day arrives.*
*Sure I’ll come to your full-day workshop, planned for three months from now. I’d love to spend a whole Saturday attending an “Empowering the Clitoris Through Post-modern Poetry, with a Three-Hour Sharing Break Out Session at the End of the Day” workshop.
And maybe we can avoid dredging up Rich Hall sniglets . . .
Some more figurative variant of buyer’s remorse?
That sounds like a pretty good Saturday, actually.
Maybe “retrogret” ?
If you enjoy poetesses writing awful stuff about The Mother Spirit and The Womb, this event is gold!
I think you’re on to something here!
Two weeks before? Sounds great!
The night before? Ohgodwhatwasithinking?!
I think it’s analogous to the universal truth about the healing effect of the passage of time against past horrible events. For future horrors, a large amount of time provides a kind of reality-defying insulation. Maybe it could be called “temporal dissonance”.
Yeah, I always forget that I hate people 
Ha! This is good!
I’m not following your meaning.
When you originally agreed, did this actually sound like a good idea? Or was it simply that you are so conflict avoidant that even though the initial idea was horrifying, you couldn’t make your mouth say anything but “Yes”? Or maybe some third thing where you didn’t even stop to think about whether it was a good or bad idea before blurting out “Yes”?
Each of these are different problems with different names for the defective thought process that got you here.
Hummm. No chance of gettin’ laid, then I guess?
Or “pregret” ?
No, that would be when you know you have to accept an invitation so as not to cause irretrievable offence (e.g., your least favourite cousin’s wedding), but you do so with a sinking heart.
Is there a word for the surprised relief you might feel when such an event turns out to be actually quite good fun?
I hate when I explain that I’m pretty sure I have plans for that day, then I’m told that the actual date wasn’t specified. 
Depends. Are you a woman? 
Or “temporal insulation”.
I think there should be a word or quick phrase for mispronouncing a word because you’ve only ever seen it written. Perhaps it could be a word commonly mispronounced in that way. (A sub-tile mispronunciation?) I’m thinking of the way eggcorn became the word for a certain kind of mondegreen. Although the difference between eggcorn and mondegreen may be suttle or absent.
How about “whatthehellwasIthinkingitis”?
I like a lot of the thinking on this.
I’m looking for a more…existential concept to be built into the word. Because I finally realized some little while back, that the me who is here right this moment, is NOT the same person who inhabited this space last month, or even earlier this morning. And the person of YESTERDAY, should NOT have the right to promise what THIS person is going to do with their time.
If that jerk who was claiming to be me in the past, really wanted to attend this insane function, let him get a time machine and do his own follow through.
Perhaps if you were to wear a diaphonous gown, African-print scarf, and Birkenstocks you would stand a chance . . . :D:D