Ideally we'd all rather this never ever ever (ever!) happen, but sometimes it does. I had it happen with a wine batch once, someone walking by it in the kitchen knocked it off and I think it was off for a day or two, no bad effects.
If you're concerned about anything airborne, feed it some campden tablets if you have any... But if it smells OK and you don't see any scum forming on the top or anything, it's probably going to be fine.
"The main ingredient needed is 'time' followed closely by 'patience'." - The Bishop 2013
"Good grief! If someone wanted to murder you, all they would have to do is ship you a 55 gallon barrel of honey and watch you document working yourself to death!" - Vance G