It's worth remembering that he human body can not feel speed, what you sense is acceleration.
In other words, when the engine thrust reduction takes place (which is standard in any departure for noise abatement as well as reducing engine wear) then you will feel an acceleration downwards. This will feel like a sinking sensation and has scared more than one person.
My first time in the flight deck in proper IMC I had a few interesting sensations when my body tried to tell me the aircraft was going weird things. However I could easily look at the instruments and see that was not the case. But my body was doing a very good job of trying to convince me we were in fact turning when we were not, or that we were descending when we were not. Very strange at first but once you're aware of it you can adapt to it.