Inception is well known for simulating all of its zero/reduced gravity scenes without CG.
There is a behind the scenes documentary where the effects team detail the various method they use – and crucially how different shots within a sequence use different methods. This means there's never a single "trick" that the eye can catch to break the immersion.
Christopher Nolan: We did it through a number of different rigs and in the final edit what you see is shot to shot to shot it tends to be a different orientation and a completely different rig in each shot and I think that more than anything else really stops the audience of seeing the trick of how this scene is done.
They used different sets for the scene, with different orientations, suspending the actors on wires to let them "fly" through the scene. The long hotel corridor was built upright, so that the walkway was vertical and the camera is looking upward from the bottom. Then they hung the actors upside down so they can freely move towards the sides of the corridor.
Paul Franklin: The vertical corridor is supposed to be the same location as the horizontal corridor, it's an identical set. The difference is that it has been built vertical standing on its end. This means we drop actors and stunt performers on wires down into the set and the camera looks up at them. They can then be raised and lowered and swing around the sides and it looks like they're floating in zero gravity.
The actors also tried to simulate the behaviour of weightless people, based on real examples.
Joseph Gordon-Levitt: In real zero-G, and I've actually spoken to people that have been in real zero-G, what they told me is they never felt so relaxed in life. What I did is the exact opposite of that. In order to make it look like that was the case I actually had to keep every muscle tight because I was supporting myself.