how hard is it to recognise that you are experiencing a delusion

http://www.independent.co.uk/life-style/health-and-families/how-hard-is-it-to-recognise-that-you-are-experiencing-a-delusion-a7776481.html

A study in the 1960s brought together three people who believed they were Christ – the results still tell us much today about how well we recognise our own delusions

• Kevin Morgan

When people experience delusions or hallucinations there is usually some loss of contact with reality whereby normal processes of thought and perception are disturbed. As humans, we are all susceptible to experiencing anomalous mental states such as this. In everyday life, for example, mentally healthy people distort reality to enhance their self-esteem and maintain beliefs about their self-agency.
When faced with negative, ambiguous or unsupportive feedback, we often respond with exaggerated perceptions of control and unrealistic optimism. In some life situations – in states of delirium, bereavement, severe lack of sleep and sensory deprivation – it is not uncommon for hallucinations to occur. The idea that delusions and hallucinations are a sign of illness or pathology tends to emerge when the belief or experience occurs outside of such situations and is held to be true in the face of strong contradictory evidence.