Ordinarily a concentration spell would end the moment you are incapacitated.
However, Gaseous Form, while being a concentration spell, has the text "The target can't fall and remains hovering in the air even when stunned or otherwise incapacitated." which – by the rule of specific beats general – would seem to suggest that if you cast the spell on yourself, being incapacitated does not end the spell, since it clearly says you remain hovering (indeed, how can that happen if no spell is in effect?).
Is it the case that
(a) if you cast it on yourself, being incapacitated actually does end the spell in spite of that specific wording, or
(b) the spell simply continues in spite of being a concentration spell, by specific beats general?
If the spell does continue working when you don't concentrate on it, how do you stop it? Just ending concentration doesn't appear to be sufficient. Do you have to specifically choose to end it?
I have seen this question Can Gaseous Form be cast on and maintained by the caster?, but it doesn't seem to directly address the seeming contradiction.
Best Answer
That sentence is there in case the spell wasn't cast on the caster; if the caster of a spell becomes incapacitated, the spell ends
This applies in the case where you cast the spell on somebody else who then becomes incapacitated. They would remain hovering in the air. However, if the spell is cast on yourself, then becoming incapacitated ends your concentration on the spell and thus ends the spell and all of its effects.
If the spell were meant to prevent you from losing concentration or to make some sort of exception to the "Incapacitated --> Losing Concentration --> Spell Ending" process, it would be stated much more explicitly.