It's all head hunger. The only reason you get hunger pains is because your blood sugar drops at certain times - it's your body's response to your usual eating times. Neurochemicals stimulated by food intake make you feel calmer and happier after eating whether you feel physical hunger or not; that is, of course, unless you were already very full, then you get a stomachache instead.
If we weren't programmed to want to eat even when we don't feel "physical" hunger, we'd be too suceptable to famine. Not to worry, when the famine comes, we'll all be the last to go.
Arline