Dramatic physiological and behavioural changes occur during the transition from wakefulness to sleep. The process is regarded as a grey area of consciousness between attentive wakefulness and slow wave sleep. Although there is evidence of neurophysiological integration decay as signalled by sleep EEG elements, changes in power spectra and coherence, thalamocortical connectivity in fMRI, and single neuron changes in firing patterns, little is known about the cognitive and behavioural dynamics of these transitions. Hereby we revise the body and brain physiology, behaviour and phenomenology of these changes of consciousness and propose an experimental framework to integrate the two aspects of consciousness that interact in the transition, wakefulness and awareness.