> Seeing something not there is hallucination and one may or may not accept its unrealness.

Though the DSM defines hallucination as an illusory percept that isn't recognized as illusory. Some theorists / clinician's use the term 'pseudohallucination' to refer to hallucinatory experiences that one knows are non-veridical.

But then the distinction between delusion and hallucination seems to break down, rather.