Second that, mostly it is a very individual thing. We've sailed on deck 8, 6 and 2 midship, forward and aft and really can't say we've noticed any difference under equal sea conditions. We have heard and been told by people prone to motion sickness to avoid watching the water during meals and focusing on things like the stage curtains in the Walt Disney Theater. Watching those things move can bring on a bought with sea sickness.
Yes the ''natural' cure to seasickness is focusing on something, often its said looking at the widest view of the horizon is best, also take in fresh air, and drink light and eat light, water for example and not fatty stuff.
Seasickness is caused by 'confusion' of messages sent from your eyes and your ears to your brain saying different things, for some this just corrects there and then, instantly, others it doesn't and thats seasickness, various treatments suppress this, but the real way to cure is fresh air and looking at the horizon.
Now thinking of that,
( please no one take this as any flame on deck 2-its not) it is best to get a outside room with a veranda, or go to deck 4 or deck 9/10.
So people prone to seasickness actually lower decks is not the best,
But again, people feel things differently, and react differently, and each cruise is different so as said before, if you have calm seas, you will think your Cat was fine, and most cruises are calm.
An interesting side to this:-
Over the years I must have seen over 25 threads asking if you get seasick on deck 2, I have seen a few threads if you get seasick Forward or Aft, now as this OP asks there must be a reason for this question.
I have personally never seen the thread with a question if you get seasick on deck 5 or deck 6 or deck 7 or deck 8, I think that tells us something re perception of seasickness.