The rule regarding ending rage is wonky. By RAW, if you are unable to take actions (stunned, paralyzed, whatever) you cannot stop raging but that is clearly not the intent.
So, go with the intent here, which is that if your first thing to do on your turn is drop rage then you are not paying for another round of rage.
The games I have played in have the house rule that at the beginning of the turn of a barbarian in a rage he can decide whether to continue raging. If he decides not, his rage ends without spending another round of rage.
I suspect that this house rule started as a misinterpretation from switching from the D&D 3rd Edition barbarian, whose rages last a fixed number of rounds and the limit on raging is the number of rages per day, to the Pathfinder rules. But it fits roleplaying the barbarian. Under the Pathfinder rules, a barbarian in a rage uses up a round of rage at the beginning of his turn, even if he intends to stop raging once he can take a free action. That feels like cheating the barbarian out of a round of rage. Or the barbarian can think ahead and stop raging as a free action at the end of his turn--Oh, I predict that my fighter buddy will finish off that last minion soon--and start his first round of fatigue immediately. That seems out of character for a rage and feels like the barbarian cheating to skip one round of fatigue. Hence, we use the house rule.
The house rule does have a tactical advantage over the rule as written: the barbarian has a chance to assess the current combat situation before deciding whether to spend a round of rage and continue raging. Assessing the situation at the end of a turn requires gambling whether he will need to rage on his next turn.
I'm now imagining a weird situation where a barbarian uses a round of rage, then drops it when she's done. Not really optimal, tho.
I can see a scenario like this. In round 1, Barbie gets mad and starts swinging for the fences. The fences fight back, and she downs two of them in round 2. She then sees Archie the archer ready to turn the BBEG who animated those fences into a human quiver.
Were she to drop rage at the end of round 2, she'd still have used 2 rounds. She's also fatigued, so any AoO she wants to do is at -1, and at -1 AC. Unless there aren't any more animated fences attacking her, this I think is just suboptimal. If she carried her rage to the start of round 3 and drop as the BBEG likewise drops due to multiple arrow wounds, then it's still 2 rounds used. But that way she can still get the benefits on an AoO.
Basically, 'Did you get your rage benefits on THIS ROUND?' might be a good question to ask there.
I'm now imagining a weird situation where a barbarian uses a round of rage, then drops it when she's done. Not really optimal, tho.
I had to do that once, with my 12th-level gnome barbarian Muffin. She had a maximum of 31 rounds of rage, due to Con 20, but after a full day of adventuring and the second combat in the middle of the night as we were trying to rest, she was down to 7 rounds of rage.
The second combat was with an Intellect Devourer. That creature had DR 10/adamantine-and-magic and resisted every spell the casters could throw at it. The party had only one adamatine weapon in the hands of a fighter, but Muffin while raging could deal enough damage to overcome the DR. Unfortunately, the Intellect Devourer repeatedly turned invisible to hide. Thus, the best strategy for Muffin was to rage and charge while the Devourer was visible and stop raging when it was invisible.
I'm now imagining a weird situation where a barbarian uses a round of rage, then drops it when she's done. Not really optimal, tho.I had to do that once, with my 12th-level gnome barbarian Muffin. She had a maximum of 31 rounds of rage, due to Con 20, but after a full day of adventuring and the second combat in the middle of the night as we were trying to rest, she was down to 7 rounds of rage.
The second combat was with an Intellect Devourer. That creature had DR 10/adamantine-and-magic and resisted every spell the casters could throw at it. The party had only one adamatine weapon in the hands of a fighter, but Muffin while raging could deal enough damage to overcome the DR. Unfortunately, the Intellect Devourer repeatedly turned invisible to hide. Thus, the best strategy for Muffin was to rage and charge while the Devourer was visible and stop raging when it was invisible.
Ah, rage cycling. I'm kind'a used to not thinking in those terms, what with my GM using that as a reason to go with Unchained. Tho I do wish rage could be done like this. That fatigue at the end sometimes feels like a stiff penalty, especially at early levels.