Comment by petecooper

>Somehow my quite limited disk space (500GB) is getting lower and lower and lower to the point where spotlight will stop working.

I know you didn't ask, but check your Time Machine snapshots in Disk Utility. If you prefer a CLI approach, this should work:

  for d in $(tmutil listlocalsnapshotdates | grep "-"); do sudo tmutil deletelocalsnapshots $d; done