Metronidazole horror stories can involve some rather unpleasant allergic reactions too. I know someone who broke out in a rash all over their body after taking it. It was itchy and uncomfortable, and they had to stop taking the medication immediately. Another aspect could be the impact on the digestive system. Some people experience severe abdominal pain and diarrhea, which can be really distressing and disrupt daily life.
Sure. One horror story is that a friend of mine had to take metronidazole and she got such a headache that it felt like her head was going to split open. It was a constant pain that even painkillers couldn't fully relieve.