Users with lower trust levels can still undelete their posts within 24 hours. However, as a TL4 user, if you accidentally delete a Private Message (PM), the site refreshes automatically. Discourse’s way of having more than one topic draft is to write a message to yourself. Such messages usually have no replies, so you can delete them yourself. So hitting the bin instead of the pencil, when you want to edit, triggers an automatic refresh. As a result, your draft is lost or you have to ask an admin to restore your deleted message.
I lost more that one draft that way. So now I try to remember to write a reply just to protect my draft.