Two recent 2016 studies on sleep, showing
- the loss of 1-2 hours sleep increases the crash risk and
- a link between loss of REM sleep and increased desire for sugary and fatty foods.
Again, of concern for those on night-shifts, varying shifts and emergency on-call workers.
A January 2017 study concludes that chronic sleep deprivation suppresses the immune system.
It can be noted that, on the other hand, as regards excessive sleep, Ibn Sina is quoted as saying, in Avicenna’s Medicine that it "...causes dullness of psychological faculty, heaviness of brain, and cold diseases..."