His chronicle of his trip, The naturalist on the River Amazons, became a bestseller when it was published in 1863.
Hot flashes and nausea are most commonly caused by hormonal imbalances in the body, most notably, by sex hormones. For women, a decrease in estrogen is often to blame, whereas in men, testosterone deficiency can create the problem. Sometimes, the symptoms occur for reasons not related to those hormones at all.
Medications can also cause hot flashes. Over-the-counter medications for sinus and allergy trouble can have an adrenaline-like effect that can trigger hot flashes. Prior to menopause, I experienced hot flashes while taking GnRH to shrink my fibroid before having it surgically removed.