Sun poisoning: 1. A nonscientific term sometimes used to refer to the serious and even potentially fatal symptoms of severe sunburn and accompanying dehydration. When used in this sense, sun poisoning is a medical emergency. Symptoms of sun poisoning include fever and chills, nausea, rapid heartbeat, rapid breathing, and possibly shock with loss of consciousness. 2. Sunburn or any skin reaction to ultraviolet UV rays. Also known as photodermatitis.