Well, I think the first thing you should do is - immediately stop what you are doing. So no more videos taken with the same Nikon camera (memory card), nor should you save other data to the card in case you may quite possibly ruin chances of Nikon video recovery due to data overwritten.
Then take the memory card out of your Nikon and use a card reader to connect to a PC or Mac machine which has installed a camera data recovery software, in order to perform a scan for the lost items.
Note: the more you take more files, the less likelihood recovery chances are!
Well,first try to find backup and if you are unable then take help of nef recovery software which get you recover all your nikon videos easily and effectively. I am pretty sure you will get back your videos