If your flooring is damaged, you may need to replace your flooring tiles. You have to also ensure that waterproofing be done with the flooring tiles installation. If you notice a damp spot that persists off and on on the ceiling, there's a 99 percent chance the drain pipe is leaking. You may need to get your pipe checked and repaired. If your neighbour's flooring is the issue and is affecting your ceiling, then other than checking on your ceiling, your neighbour may need to get their flooring fixed as well.