same explanation can be found when, say you tend to sleep with music on. and thus your ears immune and adapt to the environment. and when waking up time comes, you fail to hear the alarm.

one reason for you to be aware of such keywords because your brain has several layer of memories. it is arranged in such way that it is in accordance to the most important one on the top and so on. it is likely that you were experiencing hunger, therefore your brain matches your emotion with external factors.

and that once youre notified, you may act upon it. so the brain makes aware of such keywords to you so you would eat.

yes precisely. his brain must have has accustomed hunger > eat > food > fast food. college student perhaps? fast food = staple diet.

it could be a good thing. see most people fall into deep slumber. and thus deactivate all form of senses that signals external influence into our brain to process and so on. this is dangerous as danger happens, you have no awareness towards it. say a fire, your brain would fail to inform you to react. and you would die from excessive smoke or burnt to death.