Huge Premiere Pro error on my part.

I spent several days editing an audio track, however I pasted another file onto the same timeline track by error and have spent the past 6 hours editing that too - it seems to have overwritten what I had previously worked on.

I have tried "copying" today's work and hitting undo a million times to try and get back the original work whilst having the new work on my clipboard to paste elsewhere but the undo's stop quite early on into things.

Is there any way I can get my original work back without sacrificing today's work? I am going to be in a really horrible situation if not.

Any help would be greatly appreciated. Using Premiere Pro 5.5.

Thanks very much!