Ghrelin is one of the most important hormones, participating in the nutrition and metabolism processes (1). Ghrelin is responsible for creating sense of hunger and for "deciding" how much and which energy should be used. Ghrelin is produced in an empty stomach, when it enters the brain, ghrelin connects to the same receptors as leptin (this is a satiety hormone). That means you cannot be hungry and full at the same time.
Ghrelin regulates, whether the calories (nutrients) from food will be used for production of energy (ATP), heat, glycogen ("fast" energy) or fat. As the weight increases, level of ghrelin in the blood decreases, and this causes hunger to be felt less frequently. If level pf ghrelin in the blood is increased artificially, hunger is not bigger, but more frequent. Therefore it is considered that ghrelin is the weight control measure.
Ghrelin plays part in feeling pleasure when eating tasty food or alcohol (2). When eating for pleasure (not for hunger), level of ghrelin and endocannabinoids in the blood increases (7). Besides other functions, endocannabinoids are responsible for pleasure when eating sweet foods (6).
Higher level of ghrelin is related to antidepressant effect. On the other hand, higher level of ghrelin in this research was achieved by increasing level of stress. We know that increased stress has a number of negative consequences (3). Anyway, it looks like when facing stress, depression in difficult to experience.
If body lacks sleep, level of ghrelin increases, level of leptin - decreases (4). But you cannot compensate sleep with food, even if you are driven to. In a stress situation level of ghrelin increases regardless of the level of adrenaline produced (5). This is why people feel hungry when stressed.
What else can be said. Sleep well, take care of your inner peace, resilience to stress - and eat only when you are hungry.