Everyday, you can either have good or bad luck for various categories. I think there's a health/physical luck, and if you get bad luck for it on a day, you'll end up tripping when you run.
If you get your fortune told by Katrina she'll tell you what you can wear to prevent it or sell you a charm for 10k bells, and wearing that should prevent it.
Or you could just wait a day and hope for better luck tomorrow.