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
"When you consider that laziness and procrastination are the fundamentals of great mead, it is a miracle that the mazer cup happens." Medsen Fey, 2014
"Sure it can be done. I've never heard of it, but I do things I've never heard if all the time. That is the beauty of being a brewer!" - Loveofrose, 2014
"I tend to....um, er, experiment, and go outside the box. Sometimes outside the whole department store." - Ebonhawk, 2014