I was once at the Symphony when Tony Trishka was a guest soloist. The woman in front of me was determined to impress her date with how much she was LOVING IT, and she bounced her head up and down and back and forth. Trouble is, she was moving one way at one speed, and the performers were moving quite differently. In time she actually made me feel sick to my stomach with motion sickness.

Same thing recently at a concert of stride piano. Fortunately, I could get up and sit elsewhere.