All antibiotics work slightly differently... some work on DNA, some on cell walls, some in mitochondria of the target organism etc.

The key here is that metronidazole targets predominately ANAEROBIC cells... cells that do not get much oxygen. Therefore it is used for specific infections caused by anaerobic bacteria.
It does not affect the host cells in the same way. Bone/tooth, intestinal and vaginal infections are typically what it is used for in humans.

Fluoroquinolones are different and they disrupt DNA strands, and this is the key to their specific toxicity. They are used for all sorts of infections and have a wider range on different organisms.

Your problems may involve that virus you had, because viruses will attack the dorsal root ganglia along the spine. The herpes zoster virus (shingles) for example, does this. Dorsal root damage can appear "all over" as you describe.
Viruses can attack the brain and spinal cord too. It would depend on the person and their own immune system potential.