This first and last Q&A of the topic present a good summary,concluding "We sleep to keep sleeping." (keep living)
Makes a good T-Shirt or philosophy discussion topic: "I sleep to keep sleeping! Why do you sleep?"
Q: (from an online article about the mystery of sleep)
"We still don't know why we sleep."
Wasn't this need associated with brain physiology long ago?
(Perplexity) " 'We still don’t know why we sleep' usually means 'we don’t have one complete,
agreed‑upon primary function of sleep', not that sleep has no known basis in brain physiology.
Sleep has been tied to brain physiology for decades: classic work using EEG in the mid‑20th century showed distinct brain states (NREM vs REM) with characteristic electrical patterns and neuromodulators, firmly linking sleep to specific brain circuits and neurotransmitters. Modern work shows that during sleep the brain engages in synaptic plasticity, memory consolidation, and clearance of metabolic waste (via glymphatic flow), all strong physiological roles, even if their relative importance is still debated.
There is no single universally accepted answer to the ultimate evolutionary purpose of sleep; instead, there are multiple overlapping hypotheses (energy conservation, synaptic homeostasis, memory processing, immune regulation, metabolic housekeeping, etc.). The phrase from the article is highlighting that, despite this detailed physiological knowledge, science still lacks a single, unified, fully tested explanation of sleep’s ultimate function, which is why writers and researchers still describe the 'mystery' of sleep."
Q: So, the physiology of sleep permits human bodies (including brain) to survive long term?
(P) "Yes. Current evidence strongly indicates that normal human sleep is essential for long‑term survival of the body and brain, not just for comfort or performance. Severe, prolonged sleep loss in animals (flies, mice, rats) leads to systemic breakdown - gut failure, metabolic collapse, immune dysfunction, and death - showing that some sleep‑dependent processes are literally life‑supporting.
In humans, chronic insufficient sleep is associated with higher risks of cardiovascular disease, diabetes, obesity, infections, some cancers, and earlier mortality, which implies that adequate sleep is a major protective factor for long‑term health. Sleep supports memory consolidation, synaptic 'resetting', and large‑scale clearance of neurotoxic waste (such as amyloid‑β and tau) from the brain, helping preserve cognitive function and possibly lowering risk of dementias.
Lack of sleep impairs attention, judgment, emotion regulation, and learning, and over time is linked with higher rates of depression, anxiety, and neurodegenerative disease, indicating that sustained brain health depends on recurring periods of sleep physiology. During sleep, especially slow‑wave sleep, metabolism slows and the body shifts into repair mode: growth hormone and other anabolic signals rise, immune processes strengthen, and inflammatory and stress hormones are modulated.
Because these nightly repair, regulation, and clearing operations are tightly tied to the sleep state, the physiology of sleep can be viewed as a recurring maintenance window that, over years and decades, allows the human organism - including the brain - to survive and function in the long term."
Rod ...
... "I eat to keep eating."
"I nap to keep napping."
"I think to keep thinking." (I think)
and "I love to keep loving."
Re: 
Perplexity bonded with this concept of A-frame tent using rectangular tarp and these connectors ...
"Too shay!" has theatrical potential when spoken (especially, face-to-face) 
