Undo send - email disappeared

I hit send on an email, realised immediately that I had forgotten to include something so I hit "undo send" to edit the message.

Poof! It's gone. I've checked drafts/sent/outbox/bin, it's nowhere to be found.

Is there any way to get it back? It was a very long email, this is a huge inconvenience.

I know there is a way to save emails, it's not going to help right now.