How to use AFK and DND properly?

I leave myself on permanent afk coz i accidently forgot to put them on afk twice at my office pc and couldn't log in when i arrived back home :X

[Treloar]

I think afk should automatically turn off when you next speak in chat or do something in game or login, I have come back to game many times and then typed /afk when I went off to do something else and it then states you are no longer afk.