I think these should be unified, or the less usual condition should reference the other and note the differences.
Concentrating and stationary:
As concentrating, but the condition also ends if the creature moves (or takes an action in lieu of moving?)
I think these should be unified, have a +2 to hit, loose shield and be eligible for backstab.
I think the grabbed creature should be able to attack with a brawl, force back, disarm, or knock down, not only try to escape. Maybe at an additional -2 to hit. Monsters should be able to brawl with natural weapons.
The wording for attacks could be combined like this:
When a creature has been grabbed, the creature which grabbed it can automatically deal the damage of the attack used to grab, or perform a brawl, force back, disarm, or knock down action each round without having to make an attack throw so long as the hold continues (the opponent still receives a saving throw).
I think the grabbing creature should be able to perform other actions if its size makes it reasonable.
I also think (maybe a bit more radically) there should be a way to render a same or smaller size creature helpless through wrestling. Maybe if you grab it, knock it down and then do a successful “pin” special attack that needs attack roll at -4 and failed save?
As choking / vomiting, except the creature is able to move away from the source of nausea but cannot otherwise move.
As choking / vomiting.
I think these should have a +2 to hit, loose shield and be eligible for backstab.