There are some people on the spiritual path who reach a stage where they deliberately invoke an inner heat. And this is known as the Heat of the Mystic.
Incendium amoris - the Heat or Fire of Love - tends to be the Catholic name given to this phenomenon.
'Emotional ardour of a more intense type attended by an actual rise in body temperature'.
The ardour may be directed at a Christian figure such as Jesus or the Virgin Mary, or at God.