How does falling asleep actually work; why can you be mid-thought and just conk out?
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Sleep is a specific action your brain does.
It isn’t initiated by the part of your brain that you are actively thinking with.
So, falling asleep mid thought just means that the rest of your brain decided the sleep activity was more important, and told your thinking brain to get in on the party.
Notably, it is more likely it is more gradual than you experience, but the memory part stopped encoding memories of the thoughts. So the experience is sudden… because you suddenly no longer have access to the memories.
Sleep is controlled by 2 systems. First is sleep-wake drive. Its pretty simple the longer you have been awake, the sleeper you get, and the longer you have been asleep the less sleepy you get. A neurotransmitters called adenosine builds up during the day and dissipates at night. A new baby only has this system, so it’s one of the reasons a baby wakes up and sleeps frequently.
The second is circadian rhythm. It will keep you awake when the first system would have you sleep and it keeps you asleep when the first system would keep you awake. It uses melatonin and cortisol for this. Circadian rhythm usually develops around 3-4 months old.
You fall asleep in what is called a sleep gate. The sleep-drive wants you to sleep and circadian rhythm is producing melatonin.
Now when you first fall asleep you enter stage 1 sleep, and even stage 2 sleep, you might not notice that you have transitioned to sleep yet. When researches would wake patients up during these stages, they would say they hadn’t fallen asleep yet. This is even more true if you have insomnia. So you may still continue your line of thinking at this time.
It’s only when you get to deep stages of sleep that you would “conk-out.” During this delta wave/third stage is when the adenosine is cleared and the brain is the most asleep. So, your frontal cortex is off, and so is memory making. So even if you did continue your line of thought, you wouldn’t remember it. The next stage is REM. Some of the brain is more active at this stage, but the frontal cortex and memory are still off. After REM, you would briefly go back to stage 1 and 2. Do a surroundings check which you may or may not remember the next day. Repeat
At the beginning of the night, the cycles are the shortest, and the delta wave sleep is the longest portion of the sleep. As the night continues, the cycles get longer, and REM is the longest portion.
During the day for a nap, it works differently and it will depend on when you fall asleep. The sleep foundation can explain it better.
This is just my personal experience.
When I fall asleep, it’s sort of like my brain flips an “off” switch for both outside input *and* memory. I’ve noticed it happen when I snap back awake. I think memory only happens when you specifically think you’re receiving outside input, which can also be in dreams. Memory is a survival mechanism, so if you aren’t receiving input then you don’t need to remember. But the key is the input.
As you drift off, your brain starts to tune these things out one by one. Eventually, it tunes them all out, and your mental processes are entirely focused internally. There’s no outward input so your brain doesn’t need to remember what is happening. Then you’re asleep. We know the brain stays active at night and I think this is why. The internal monologue (or non-worded equivalent) continues on till dawn.
Then you wake up and your brain tries to grasp all its surroundings, resulting in losing whatever thoughts you had before you woke. That’s why dreams typically fade with short term memory unless you think about them a lot.
I mean, you can’t. That’s the problem with falling asleep, your mind has to be still and thoughtless.
Not a sleep scientist but decided to share my anecdotal experience.
I experimented with lucid dreaming when I was young, and later in life for unrelated reasons started to have sleep troubles, which led me to using various podcasts to help me sleep. That gave me opportunity to experience falling asleep from two different angles. Disclaimer, I am just describing how it feels and speculating.
First of all, if you focus you can stay conscious as you fall asleep. It’s a bit freaky. You gradually lose sensation in your limbs and your eyes start moving violently underneath your closed eyelids.
So it’s a process completely separate from everything else — your body is shutting down.
Other thing, if you can’t sleep — half of you lying there in bed is a dream. I used podcasts to fall asleep and I noticed that occasionally I am lying there in silence and wondering — hey, where is that podcast. And suddenly, the sound appears out of nowhere. I woke up.
You don’t even notice how reality fades away.
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