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.
Nausea often follows hot flashes because abrupt changes in serotonin can also stimulate the area postrema - a part of the brain that controls nausea and vomiting. As the area postrema is located right next to the hypothalamus, often what disturbs one will also impact on the other.