It depends. Do you have the undelete (dustbin) package installed and is "Create backup files in dustbin for decrypt and shrink"? set to Yes in the Auto-Processing settings?
If so, it's probably recoverable. You're going to get good/have to learn some file management skills if you're not that technical. I find the easiest way to do it is using the file explorer on a Windows PC, but you need the Samba stuff installed on the Humax.
It's very difficult working blind. You'd need to produce a recursive directory listing from the command line and get it on here somehow.
It sounds like something automated has done it. What packages have you got installed that may do stuff like this? e.g. sweeper, flatten, series-filer etc.
Were they correct previously?
It (almost) goes without saying, that if you are going to experiment with something, you do it on a copy and not on your only original!