When it says "the only action you can perform", it just means "while you have stun, your list of available actions is one thing: remove this card".

Standing up when knocked out ends your turn, but Stun doesn't.

If you are Stunned before you start your turn, you'll have 2 actions available. However, your only available action is to remove the stun. So your first action will be to remove it. However, you still have your second action (removing the card doesn't end your turn), and since Stun is no longer on you, your available actions become back to the standard list.

IE, the "only" is referring to your options, its not referring to the number of actions you get on a turn. That's the problem with English sometimes, though But this has been officially clarified in the past.

Got it, thanks. You see, if this is a problem for english native speakes, go figure how a portuguese native speaker can suffer

Side note: I found the quest "A fat goblin" much harder to be winned by the players.In the first encounter, as an OL, I choose a group of barghests as the open group. They totally blocked the way to the heroes to reach the farm. Since the goblins have high speed was very very easy for them to run awy with the crops. I could save only one (unique? lol)

The second encounter was close, but the OL still wins. I could damage Splig in 20 hp (he has 25 in that adventure, according the rules), but he managed to knock out Grisban and found a scape route, while Tomble and Ashrian (that bad girl!) miserably missed their attacks, and the overlord uses the dash card to help...