Levaquin and stomach flu

My mother, age 73, has always been in excellent health. She was prescribed Levaquin for an upper respiratory infection. She immediately became nauseous and slept all day. She is the type of person who barely gets nauseous with stomach flu. Within 3 days of taking the Levaquin she began to have tremors. She can no longer write legibly. Her entire upper body and voice quiver constantly. Her legs feel week and quiver "from the inside" and she has no energy. She took the Levaquin for only 5 days. She stopped over a month ago and still has tremors and lack of energy. I don't believe people are being warned of the possible side effects of this drug.