I seem to have lost everything in my Thunderbird email account

I rebooted my computer because one program failed to respond, and the email inbox that I had open with a large number of messages in it, suddenly was not available. All I had under local folders was trash and sent. When I tried to send and collect a test message, it said it could not be saved in the sent folder, and, that being the only folder by which I thought I could open / find the other folders, did not appear in the sent folder.