It's possible that it's not literally about less sleep, but about worse sleep

A recent 2024 review in PNAS argues that disturbances in sleep timing and continuity, rather than pure lack of sleep alone, are pervasive across many psychiatric conditions, including anxiety, depression, and psychosis. Poor or misaligned sleep can trigger or worsen symptoms, while those very symptoms further degrade sleep, creating a vicious cycle. Because modern lifestyles (e.g., round-the-clock connectivity, exposure to artificial light at night) directly disrupt our circadian rhythms, it is plausible that a portion of today’s social and health challenges, especially those related to mood and mental well-being, stem partly from these sleep circadian issues. They think that targeting sleep and circadian factors brings tangible improvements in mental health outcomes. If improving sleep quality improves outcomes, then the poor sleep quality could be argued to be the source of these health problems.

I think you need to clarify what you mean by modern.

Are you asking if lack of sleep causes problems in comparison to 1960? Or like 1690?

It's not quite related to your question, but fascinatingly, some studies have found that that if you make people with clinical depression stay up for 36 or 48 hours or, their symptoms actually progressively improve! Obviously, this isn't incompatible with the idea that consistently getting poor sleep for long periods of time might have deleterious effects on one's health. Here's a neat writeup by Scott Alexander: https://www.astralcodexten.com/p/sleep-is-the-mate-of-death

No.

To see this, you simply need to make a list of modern problems. Then separate them into "May be caused by inadequate sleep" and "Not sleep related."

• Climate change? Not sleep related.

• Disinformation campaigns? Not sleep related.

• Gullible voters? Not sleep related.

• Every goddamn transaction asking for a tip? Not sleep related.

• Pretentious twits on Manifold? Okay ... maybe I should get a bit more sleep.