We just don't want to hear that nasty sound. A person has set the alarm for 6:00, and the body already subconsciously knows that it is better to wake up before that in order to avoid negative emotions.
This happens thanks to the internal clock (biological). If you have an important meeting, in most cases you think about it a lot and set yourself up to “not oversleep.” I don’t know the essence of the process (I’m just setting out observations of myself): most likely , the brain adjusts the cycle and awakening. This tool, with the proper skill, can and should be used.
And it works everywhere - it is enough just to clearly scroll in your head what and when to do, and it is desirable to imagine, how you will do it. Whether it is waking up or not forgetting to buy something, or calling someone, 99% of the time you will succeed, and you will remember or wake up.
You wake up not only 5 minutes before the alarm, but also many times a night, you just do not remember these awakenings. If an important meeting, a night flight and so on is stressful, then there are more such awakenings, and the period between them is shorter. But this applies to cases when you need to get up earlier than you are used to. In other cases, awakening is regulated by the circadian rhythm (biological clock)
Well, this concerns not only meetings, but in general. If a person needs to wake up, say for a train at 3 am, then he will also wake up in most cases before the alarm clock. I won't give an exact scientific answer (I don't want to go to Google and copy from there), but the point is that our brain has its own clock, its own alarm clock, and when necessary - it works :)
Just eat and all.
Well, since you are minus, then:
German scientists have managed to find hormones that send a signal to the brain, the action of which can be compared to the mechanism of an alarm clock.
The hormones adrenocorticotropin and cortisol send a message to the brain that is responsible for awakening in the brain. This explains why some people may wake up on time without an alarm. Both hormones are produced by the body in anticipation of stressful, extraordinary situations. For example, school exams, conflict situations, giving a presentation, etc.
In the same study by German scientists, it was also recorded that the level of hormones rises in the later stages of sleep, provoking the expectation of the moment of awakening. Scientists are generally unanimous in the opinion that sleep is a state of unconsciousness, however, all the same research has shown that the brain is in a state of alert consciousness. The researchers believe that based on the scientific data obtained, it is possible to develop a course of therapy for those who have difficulty getting up early, work in different shifts, or, due to work needs, are forced to sleep at different times of the day.
The feeling of congestion does not go away.