I usually wake up just ahead of my alarm. What's up with that?

Maybe I missed it in the article, but my main explanation for this phenomenon is based largely on me waking up before the set time and looking at the clock. I assume that I would adjust my slumber to the remaining time before the alarm. I don't need to hit 8 hours ahead, just one. Indeed when my sleep phases are deeper and longer, it's unlikely for me to wake up just before the alarm.

Seeing this tied to a stress hormone makes sense. It is intriguing to think that we can set an internal alarm. On the other hand, I would assume that this too is regilated by external clues. I remember how I could gauge morning progress just from the noise level when I was living close to a street.

I do wonder what is healthier though: preparing to get up by lightening our sleep ahead of the alarm, or getting more deep sleep but ripped out of it suddenly.

Would be nice to record a video of the face of the sleeper.

Because it's possible that they had a look at the clock tens of times while still half-sleeping, only for the last one to trigger a wake up (and the only time remembered).

Anecdotally, when I get extremely consistent sleep, like a week or more of going to sleep in the same 5-15 minute window and having an 8 A.M. alarm, I start to wake up at like 7:58/7:59 am. I suspect it's just my 'biological clock' falling into a routine.

The actual biological mechanisms responsible for this is a question for someone more educated than I am in that space.

Notable anecdote factors: I never consume caffeine after 3pm, I use taped down double layer blackout curtains so there is virtually no change in light level, and I have no blue light / stimulating mental activity an hour before bed.

It was over 20 years ago in college when I learned I had this ability. I was overloading classes in support of a double major and had far more work than I could handle. I eventually realized I could wake myself on demand within 10 minutes of a given time when I'd set an alarm to wake up at 3:30am. I kept waking up before the alarm.

Later in life, I did the same to wake myself up for work, and kept waking within a few minutes of my alarm going off. I eventually stopped setting an alarm and haven't used one for at least 15 years, even when traveling, having to get up an an unusual hour, or not having a consistent bedtime.

Even now, I fall sleep anywhere between 9:30pm and 1am, but wake up just before 6am on the three days a week I go to the office. This works just as well in the summer as it does in the winter. Other days I generally just sleep until I wake, which is usually 7:00 to 8:15am or so.

An anesthesiologist could tell you. You see, general anesthesia has three basic components. The first immobilizes you. The second blocks your memory. You can imagine what would happen during surgery with either of those two missing. The third is an ordinary pain killer like morphine or fentanyl. Waking up is just the first thing that happened after they turned your memory back on.

So the truth is, this phenomenon says that you were probably lying there in light REM thinking about getting up for a long time before the alarm went off, or checking the clock every few minutes between dreams until it was time to turn your memory back on.

I did this too before every morning swim practice, except when I didn’t finish the deep sleep cycle.

My guess, it's a mix of subtle changes in temperature, external noise patterns and light that are detected for the rough estimation, and then is when stress kicks in, and we do a lot of micro time checks with eyes slightly open that we forget, personally I remember checking the time semi consciously like 100 times, before "accurately" stopping it just one minute before, but other times I experience opening the eyes one second before the alarm rings and it feels so amazing that I suspect I forget everything else.

Also explains why insufficient sleep makes people vulnerable to getting sick. Cortisol is a potent immunosuppressant. With insufficient sleep, it stays elevated

Could it be related to the leap year? Our bodies don’t account for it, it’s us humans that do this artificial adjustments. A minute a day is roughly equivalent to a day every 4 years.

You have pretty accurate internal clocks. You can learn to wake up at a particular minute, without any alarm clock at all. It's not hard.

You've become one with the machine.

My explanation is perhaps bad statistical reasoning. You never really know what time you would have woken up naturally without the alarm. So those instances get forgotten. All that you think about are the times when you get up right before the alarm. And I suspect people are usually are not within a minute, but more like 10-20 minutes.

Tldr nobody knows

When I was young I could give myself a time to wake up and wake up at that time. As I've gotten older I've lost the ability.

But I would use it to get up 30 minutes early to play NES before school. My mother would make me go to bed at a specific time, but if I was working on a particularly hard spot in a game I'd tell myself to get up 30 minutes earlier and spend that time playing.

I also used to lucid dream very frequently. I'd recognize it as lucid dreaming and actually start manipulating the dream. What's always been interesting to me is that dreams have rules to them, so even manipulating them there are limits. Sometimes I could fly freely, sometimes I could barely get off the ground.

Also, past a certain point in my life I completely stopped having nightmares. A nightmare has a "feel" to it. Even if it starts off pleasant I recognize that feel and simply step out of it.

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So, we may not have an explanation for, but it absolutely happens.