The Black Death, unemployment, World wars
He is not getting enough sleep
Cause and effect and that’s the answer
Remaining healthy in Elizabethan England was a challenge.
This is the central idea of the passage. We know this because it says, "there is no concept of 'health and safety'. Other details that reveal this as a central idea are "contemporary standards of cleanliness will worry you", "People die every day from unknown ailments", and "Infectious diseases periodically kill thousands". This all shows that remaining healthy in England was a challenge.
