WTF happened to my dishwasher? aaarrrggh?

I was unloading the dishwashing machine, had both shelves pulled out, and the entire unit fell out! How the eff did that happen?! It didn't fall to the floor, thank goodness, but it almost did. I managed to push it back into its cubby hole. But can I use it now? Or does it have to be bolted in? I've been in this place for about 7 years and have used the machine without problems all that time. The only cause I can think of is that the maintenance man came in to replace the dish disposal and possibly had to move the dishwasher to do so.