After opening file, file wrong

Hi,

I am pretty new to LibteCad but slowly getting the hang of it. So far I really like it but unfortunately after hours of work on one document, regularly saving it and happy for my progress. I woke up this morning and opened the file. It was not what I had ultimately saved last night. What went wrong? Has this happened to anyone else? What can I do to prevent this and what can I do to get the drawing back I had yesterday?

Thank you!

Simon