Demons and voices are "makyo":
https://en.wikipedia.org/wiki/Makyō
They are distractions that come from the thinking mind. If your mind is still, they aren't there by definition. The stillness is the deeper reality of these experiences - the thing that is ALWAYS there when the mind is allowed to stop.
Many experiences of all kinds occur during meditation. Most of them are blissful. Some people have supernatural experiences, some don't. It's good to have recourse to a proper teacher to check in with who has seen and understands these experiences, so that when things like this happen they can be framed in their proper perspective and there is some tuning of your practice where problems arise.
@Cadcam, if you are continuing to experience anhedonia you should really be in contact with a mental health professional.
