Selfhood is linked to brain processes that enable the experience of a person as a distinct entity, capable of agency. This framework naturally incorporates a continuum of both non-conscious and conscious self-related information processing, and includes a hierarchy of components, such as awareness of existence (core self), embodied self (sentience), executive self (agency/volition), and various other higher-order cognitive processes. Consciousness relates to, but is not congruent, with selfhood; understanding the processes required for selfhood can explain the partial consciousness seen in anaesthesia. Functional-brain-imaging and electroencephalographic studies in sleep and general anaesthesia have shown differential effects of anaesthetic drugs on various specific self-related functional brain networks. In particular, drug-induced selective impairment of anterior insula function suggests there might be a crucial difference between anaesthesia and natural sleep when it comes to the salience network. With increasing concentrations of anaesthetics, it is not uncommon for patients to become depersonalised (i.e. to lose sentience and agency), but retain many higher-order functions and a disembodied self-awareness, until quite high concentrations are reached. In this respect, general anaesthesia differs significantly from physiological sleep, where it appears that loss of agency and sentience parallels, or lags behind, the decrease in self-awareness. Interestingly, connectivity within the posterior brain regions is maintained even to quite high concentrations of anaesthetics, potentially representing a pathognomonic marker of the core self that possibly is involved in maintaining a reduced energy state of homeostasis.