One reason may be due to inactivity. The other more important reason is that boredom and subconscious messages trigger eating when not hungry. Advertising and food programmes prompt snacking and mindless eating
Many people will stay up late watching anything on the TV in an effort to capture some downtime, due to long working hours, resulting in shorter sleep.
Short sleep is associated with higher levels of the appetite-stimulating hormone ghrelin and lower levels of the appetite-sating hormone leptin. Short sleep can also induce insulin resistance, and this might lead to increased hunger and weight gain. Also the longer someone is asleep the less opportunity to eat, even though there is reduced activity. Sleep helps with our repair metabolism which is vital to stressed individuals, the very people often sitting up late watching TV (with alcohol?)
Tiredness (the next day) has also been shown to decrease activity levels and trigger unhealthy food choices.
So set the recorder and get some sleep!!