what is the relatoionship between physical environment and mental state as it pertains to the conditions of sanity and madness?

First of all the wilderness the men were to travel through was well known to create enough stress and apprehension that some men would go crazy. In the beginning the doctor questions Marlow about whether or not his family has a history of mental illness and specifically tells him that he'll need to keep it together on the trip.

We are also in a physical environment that runs rampant with tropical diseases. Many cause high fever........ thus many would be out of their heads before finally succumbing to the disease or getting better.

Kurtz becomes ill and suffers with tropical diseases. Eventually, his sickness combined with complete isolation serves to unhinge his mind.