You could easily be forgiven for believing that just like a psychopath, a narcissist has no conscience either and on the face of things it usually does very much seem like this is the case. However, a narcissist (someone inflicted with Narcissistic Personality Disorder or any other form of malignant narcissism) does not suppress their guilt or shame in the same way that a sociopath/psychopath would.
Whilst it seems like a narcissist has control over their conscience, the truth is that they usually suffer with an overwhelming but well disguised conscience and they experience such high levels of shame and guilt that they find them unbearable and too emotionally painful to cope with. They do not openly display these emotions and just like they do with their thoughts and their deepest secrets, narcissists keep their feelings covert and under cover. However, unlike a psychopath (some of whom are capable of literally 'switching on' and 'switching off' their empathy at will), this is often a gradual process which happens in cycles over time. It can, however, also happen over the course of a night or two.
Due to the fact that narcissists ignore and suppress their true feelings of guilt and shame, this can often give the impression that they are completely devoid of emotion and they may often appear to be in a zombie-like trance. In actual fact, the opposite is the case. Their feelings are so strong, so powerful and so painful to deal with that they put them to the side and hope that those emotions fade as they force themselves to forget about the memories associated with the events that caused those emotions in the first place. They do so by simply choosing not to think about or remember those events. Such events could involve emotional blackmail, psychological abuse, one-night stands, secret affairs and/or something more extreme.
The easiest and best way for a narcissist to bypass their conscience is by ignoring their feelings (and associated memories) of guilt and shame in the day and by sleeping them off in the night and whenever else they can. If they have committed a particularly shameful act, they may keep people at length emotionally and may begin to sleep excessively until their conscience fades. For smaller shameful acts, they may sleep for one night then attempt to put their feelings of shame and guilt behind them and treat the next day like a fresh new start... until next time.
[ Image: John Hain at Pixabay - Public Domain - https://pixabay.com/en/self-criticism-thoughts-judgements-440303/ ]