Core below 37 °C → reasoning problems. Below 35 °C → shivering ceases, apathy. At 39 °C → impaired physical and mental performance.
Extreme cold → sleepiness with contentment or apathy; earliest feature is apathy. Response to cold is intense vasoconstriction; to heat, sweating and vasodilation.
Man has NO effective natural protection against intense cold. Heat acclimatisation takes a fortnight.
Tropics: avoid all five — ice, lake swimming, unpeeled fruit, local ice cream and salads, short clothing at night. Contaminated water → typhoid, cholera, dysentery, hepatitis A. Hepatitis B/C from unsterilised needles. Yellow fever from a mosquito. Tetanus from spores via a skin puncture.
Ditch PARALLEL to the swell. Fire in flight — most deaths from suffocation from fumes. Fuel on skin — copious water, no soap.