Disappearing email

When I compose and send a gmail from my MacBook, it no longer goes to the recipient and it completely disappears from my computer. I spent a couple hours this morning composing email, all of which appears to have vaporized. I use a couple of gmail accounts on the Apple Mail interface. I looked at the accounts on a web browser, and there is no record of any of the sent mail there, either. Any ideas on how to fix this -- and, hopefully, recover my mail?