A hot flash is a sudden sensation of intense body heat, often with profuse sweating and reddening of the head, neck, and chest. These symptoms can occur with mild to severe heart palpitations, anxiety, irritability and, rarely, panic. Hot flashes are the most common symptom of a woman's changing estrogen levels around the time of her last menstrual period (menopause).
The biochemical cause of hot flashes is not well understood. Hot flashes are more common at night than during the day and are a common cause of sleep problems for perimenopausal and postmenopausal women.
While some women will never experience hot flashes, others begin having them in their 30s. Hot flashes are most frequent and intense during the first 2 years of postmenopause, when estrogen levels have dropped below a certain point. Sleep patterns usually improve within 6 to 12 months after hot flashes begin.
WebMD Medical Reference from Healthwise