You're speaking with Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply.
I'm sorry that your question wasn't answered in a timely manner. Tail quivering can indicate alertness and interest when the tail is held down and being happy to see you when the tail is held up. It's not an indicaton of pain. Take a look here for more "tell-tale" tail information: https://www.google.com/search?q=cat+tail+meanings&rlz=1C1CHFX_enUS705US705&tbm=isch&imgil=MoEsGMCvj3pQTM%253A%253BbbSYT4vibX0SZM%253Bhttps%25253A%25252F%25252Flifewithchcats.com%25252F2013%25252F04%25252F22%25252Funderstanding-your-cats-body-language-the-tail%25252F&source=iu&pf=m&fir=MoEsGMCvj3pQTM%253A%252CbbSYT4vibX0SZM%252C_&usg=__SXQpwaRr9hQ1lg_d_xTTSTL65Do%3D&biw=1920&bih=974&ved=0ahUKEwjnpvqk98PPAhUL1oMKHcdkDV4QyjcIOQ&ei=2RX1V6dWi6yPBMfJtfAF#imgrc=MoEsGMCvj3pQTM%3A