What causes dizziness, hands to shake, and reflexes to slow with any amount of caffeine?

Individual sensitivi: The only answer this would be the you have individual sensitivity or susceptibility to this caused by the caffeine. It is well-known that caffeine worsens hand tremors. In addition, it would generally increase reflexes. However, when it comes to chemicals in the brain, no two people are alike. This is also why you would have dizziness when other people don't.