Urgent help needed - how to revert a bulk image name process?

Apologies - the Urgent in this is only because I'm unsure whether any action may need to be done before I close down in about 6 hours or so.

Basically my problem began in Picasa 3 where I watched a short vid then decided to change the filename. That done I closed the preview & went back to the main program where I discovered that Picasa had somehow decided I wanted the entire folder of images renamed so it has worked through the 500+ images and renamed each one as Filename001, Filename002, Filename003 and so on which as you can appreciate is now causing somewhat of a major headache for me. It would take me a good few hours I would rarely have to go through and rename each one manually, so my question basically is - is there any method or program that can undo the action as I can't find any means of doing so from within Picasa. All other options I've found in my searches are mainly to achieve pretty much the same i.e. bulk rename as Name1, Name2 etc so are of little help.

Anyone any suggestions what else I could try?

I assume you don't have a Backup to fall back on. I use these two bulk renaming tools. You can see if they help. This is drop dead simple to use - http://www.fauland.com/af5.htm
This one has a more complicated interface but a couple other options - http://www.joejoesoft.com/vcms/108/

Backup - oh yeh one of those things you're supposed to do regularly - oops!!

Good point actually as I've been remiss in doing backups of any kind but yes actually I prob do have some of the files but not all backed up so at least that might be of some use.

But yes, I'll go check out your suggestions & thanks SO much for responding so fast - I was worried nobody might bother to reply as I appreciate firstly it's not really a Win 10 issue & secondly is one of those problems few would maybe ever encounter.

Will update you shortly :)

Yes, those bulk rename utilities will help you a lot than you can imagine. :)