A wrench in the works

I had one of those unexpected things come up today that completely derailed my plans for the day.  I had a doctor's appointment for an insulin trial I'm doing, and since I'm almost done with it, they wanted to dilate my eyes.  It was going to be a scheduling nightmare to try to come back and do it a different time, so I changed my plans for today (which included a riding lesson) and just got the eye exam out of the way.

Unfortunately, not only can I not ride, I can barely see my computer screen.  Every time I get my eyes dilated, it usually takes until evening to wear off.  I can't see close up right now with my glasses — in order to see my computer screen, I have to take off my glasses, and then lean waaaay forward since my vision is so bad.  Not a particularly comfortable way to work, so I'm going to take my usual approach and read (without my glasses) or nap for an hour or two, or at least until the worst is passed.

Are there things that come up sometimes that make it impossible for you to work?  Where do you draw the line and say, "Forget it, I'll do it later"?