You may not have even realised this but Discourse allows you to store draft replies to topics and PMs.
In fact, if you went into every topic, started a reply but then left it, you’d have hundreds of active drafts.
It’s quite easy to forget where you were until you try to reply in a thread where you have already started a draft post and when you hit reply, you see your old draft waiting for you.
Anyway, Discourse now gives you an option to see all of your outstanding drafts and to Delete them or Resume editing them to turn them into posts.
Visit your Profile page and then look within Activity and Drafts.