How did your try to open it ? Perhaps you right-clicked and chose an archiving / deleting option by mistake or it was moved to another folder. Check your Trash or other folders, perhaps use globals search to look for it.

I found it in a trash folder that was not associated with that gmail account. Not sure how it happened, but I was glad to find it. Thank you for your help.

I have this same problem but my message in the Draft folder was actually information I stored on the page and so it was very long - would that have anything to do with why it just disappeared? It happened twice before and I found it both times in another folder but this time I've checked everywhere. Does anyone know where I can check or what to do next? It's very important I locate this message. Thank you.