This was asked in a viva.
So I did my usual Googling and found this as a satisfactory answer :)
Several mechanisms may be involved in the development of circadian abnormalities in cirrhosis, including the effect of gut-derived toxins on the brain and decreased sensorial inputs that entrain the circadian clock such as insufficient light exposure, social isolation, or low levels of activity and retinohypothalamic and endocrine (e.g., melatonin) abnormalities.
The sleep-wake cycle is one of the functions regulated by the circadian clock, the suprachiasmatic nucleus of the anterior hypothalamus, which has efferent connections that influence a large array of biological functions including the secretion of melatonin from the pineal gland.
For people who sleep “normal hours”, natural melatonin production peaks between 2 am and 4 am, with the peaks becoming smaller with advancing age. Normally melatonin is a natural sleep-inducing agent. Because daylight reduces melatonin production and blood levels of melatonin are usually high at night and low during the day.
In patients with cirrhosis, the diurnal plasma melatonin profile shows a significant delay in the onset of plasma melatonin increase and a delay in its peak nocturnal level. This displacement of the melatonin profile could be a reflection of a shift in the phase of the circadian clock.
