How to fix level corruption?

[Stroyed]

I just, on accident, opened a map that I made in Hexen format in Doom 2 format. Now all the linedefs, sectors, and things are everywhere in a jumbled mess. I tried reloading it in Hexen format to no avail. How do I fix it other than re making the map if possible?

[MaxED]

Unless you have saved it 3 times after doing that, you can restore it by renaming the newest backup file from "yourwad.wad.backupN" to "yourwad.wad".

[Stroyed]

Thanks for the help but I was able to fix it.

[Grey Rook]

Thanks for the help but I was able to fix it.

So, how did you fix it and what did the problem turn out to be? Just for posterity.