How does saving a project with another project work?

[Robbie34135385e7mh]

I have been working on a massive editing project that has just reverted to my template file (a project I start with that just has all my base template layers/files/effects etc) which is really infuriating. 

The only thing I can think that must have happened must be that I opened my template file whilst working on the other project and perhaps I clicked save whilst in the template section, which saved my current file as the template one? Would that not just save the original template file and leave the current file unsaved? I would expect that doing this would not save all my progress, but I don't expect my current file to completely revert to its original state.

This is the only thing I can think as it's such a strange way for a file to corrupt, it's literally deleted everything apart from the template files I usually start with. 

I assumed auto save was saving things but I'd reached my 200 files limit. 

[Peru Bob]

Check your backups.