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I think a rotating frame would have both a centrifugal force, mimicking gravity, and what is called a Coriolis force. So, for example, if you would throw a ball straight up in the air in the rotating space station, you would see it move sideways too, because the outside of a wheel always rotates faster than the inside.

It's possible that the people in the space station could feel this Coriolis force, hence the reason for the discomfort.

I'm speculating, but the speculation is based on actual physics :).

Your physical experience of gravity on a planet and artificial gravity at the outside of a rotating wheel might be different based on the following.

The force you feel from a planet is $G*m_{you}*M_{planet}/r^2$ (Gravitational constant times your mass times the mass of the planet, divided by the distance $r$ from you to the center of the planet, squared.

The force you feel from the rotating wheel is $m_{you}*omega^2r$ (your mass times the angular velocity (squared) times $r$, the distance from you to the center of the wheel).

So, suppose you are on a planet (which would normally have a very large value of $r$--meaning, you are a long way from its center), and you are seated, then you stand up. Your head has moved from $r$ meters to $r+1$ meters (your head is now 1 meter farther from the center of the planet). So, on earth, you've moved from about 6.4 million meters away to about 6.4 million meters...plus one! That's going to make a change in the force on your head that's probably way too small for you to notice.

On a man-made rotating wheel, you're going to have a much smaller value of $r$ (assuming the wheel is way less than the size of a planet). So $r-1$ meters (keep in mind, when you stand up inside the rotating wheel, your head is closer to the hub of the wheel, so it's a change to $r-1$ instead of $r+1$ as it would be on the planet) might be different enough from $r$ meters to be something you feel, and, if you spent a lot of time there, or were born there, or whatever, you would get used to things (like your head) being "lighter" when you stand up. If that was your "normal", then it might feel really strange to you when that didn't happen in Earth's gravity.

For a non-technical answer, remember when you were a kid on the playground? (Yes, I know I'm making what's perhaps a parochial assumption.) If you sat on the merry-go-round (this: https://en.wikipedia.org/wiki/Roundabout_(play) ) and got the other kids to push it around really fast, you could feel the "gravity" pulling you outwards. But because you were also going around in a tight circle, the fluid in your ears sloshed around, and so you got dizzy.

Now scale this up to a moderately-sized space station. You might still have some effect on the ears from rotation (how much depends on the size), but because you've been there a long time, your body has adapted to this as being normal. When you shift to "real" gravity, the rotation effect goes away, but to your body this is now NOT normal.

(Whether this would actually happen I can't say: AFAIK no one has tried it, but it's certainly plausible enough for SF :-))

You would be unlikely to notice any difference unless the spacecraft is fairly small.

For example with 50m radius there is only a 2% difference between 50m and 49m. The station in this case would be spinning at 4.25 rpm to generate 1G.

Experiencing rotational forces and fixed direction gravity at the same time would be weird.

A person under the influence of gravity experiences a constant acceleration. A person in a rotating reference frame experiences a constant magnitude acceleration, but the direction is changing constantly.

This means that if you are experiencing both at once, and the axis of rotation is not parallel to the direction of gravity, the total acceleration that you feel will be constantly fluctuating. It's more or less equivalent to the fact that if you swing a bucket on a rope in a vertical circle, the tension in the rope is higher when the bucket is near the ground than when it is at the top of the swing.

Depending on how fast the rotation of your station is, this could make the transition period feel like a rollercoaster.

Of course, the logical way to transition reference frames would be to leave one, enter zero-g, then enter the second. That would avoid the roller coaster effect. But if they skipped that process then I could easily see people emptying their stomachs during the process.

In my opinion there is mechanical difference in which the rotation affects you in those two cases (you rotate on planet while not on poles). On planets surface the mass pulls you inward and the planetary rotation lessens the force applied to you. On the station the rotation works the other way, basically creating gravity from nothing.

Have a nice day.

Please have a look at "Why don't spaceships have artificial gravity" by SciShow Space on YouTube. It explains the topic way better than I could ever do.