Isn't vertigo a disease within the vestibular system? Flying in the clouds can cause spatial disorientation, which is the inability to correctly interpret aircraft attitude, altitude or airspeed, in relation to the Earth or point of reference.

My first experience with spatial disorientation was about 1 second after entering the clouds for my first time. Its nothing scary, but just a strange sensation. Trust the instruments and the feeling goes away. Occasionally I still get a mild form of "the leans". I believe it is normal.