Loss of all my filed emails

After starting Thunderbird I set up a list of subheadings in the local column left of the inbox. I filed all my important emails into appropriate sub-headings (events, invoices to do etc etc). Suddenly all of them (including the scam subheading ) have disappeared and all there is Local and delete. Please can you advise me where they have all gone and whether I can retrieve them because losing them all would be a bit of a disaster Thank you