sorry to hear that.
sadly, as long as you haven't backed up your world, there is no way(as far as i know) to recover this world.
it probably was due to a powershortage that turned off your pc/laptop, you roughly turning off your pc or an old or demaged harddrive.
I suggest for the next map you back up every time you've played or build something and always keep the last two backups.
i know it's annoing but it can realy be a lifesaver sometimes.
but good luck for your next world :)