Serious side effects of Levofloxacin: central nervous system effects, including seizers, hallucinations, nightmares, depression, confusion, paranoia, suicidal thoughts, and tremors; gastrointestinal infections and disorders; potentially irreversible peripheral neuropathy (damage to the nerves outside the brain and spinal cord); serious heart rhythm changes; joint problems; changes in blood sugar; sensitivity to sunlight; severe diarrhea from the difficult-to-treat bacteria Clostridium difficile.