On 10 December 1831, as he waited in Plymouth for the voyage on HMS "Beagle" to begin, he suffered from chest pain and heart palpitations, but told no one at the time in case it stopped him from going on the survey expedition. During the voyage, he suffered badly from sea-sickness during the eighteen months he was at sea, but he spent much of the three years and three months he was on land in strenuous exploration. In Argentina at the start of October 1833, he collapsed with a fever. He spent two days in bed, and then memories of a young shipmate who had died of the fever persuaded him to take a boat down river to Buenos Aires, lying ill in his cabin until the fever passed. On 20 September 1834, while returning from a horseback expedition in the Andes mountains, he fell ill and spent the month of October in bed in Valparaiso. In his journal for 25 March 1835, while to the east of the Andes near Mendoza, he noted "an attack (for it deserves no less a name) of the Benchuca, a species of Reduvius, the great black bug of the Pampas", which are associated with transmittal of Chagas' disease.