my point was that the characters would know immediately if gravity was not "normal" in the Skimming place. The same reason why, if you go to the moon and gravity is different, you'd be jumping all around going "holy shit!" You can feel it.

Whether gravity there is a property of the Skimming world, or if it's a manifestation of the channelers' minds is something that we don't know. What we do know is that, in every instance we've seen, gravity has existed. We know this by virtue of the fact that none of the characters indicated anything out of the ordinary, which they undoubtedly would have.