Why does a sick person's body temperature rise at night?

When ill, your body has to fight the infection with antibodies. To speed up the production of these, the body heats up, as higher temperatures mean faster chemical reactions to do this, your body 'turns up its thermostat', and makes your body think that it is colder than it is, so your body heats up: it makes you fell cold, so you put on layers, turn up the heating e.t.c. (this is done by a small gland near the centre of the brain, the hyperthermos (not sure about spelling)). When asleep, you thermostat does not, like normal, cool down, but stays at the same level. 

So, at night, the body thinks it is cold, and cannot add layers (as you are asleep) so uses energy heating you up. This is one of the reasons that a sick person is often tired and hungry.

Health

Health is the level of functional and/or metabolic efficiency of a living being. In humans, it is the general condition of a person in mind, body and spirit, usually meaning to being free from illness, in or pain. 

Personal health depends partially on one's active, passive, and assisted observations about their health in their everyday life. The information gleaned from such observations may be used to inform personal decisions and actions (e.g., "I feel tired in the morning so I am going to try sleeping on a different pillow"), as well as clinical decisions and treatment plans (e.g., a patient who notices his or her shoes are tighter than usual may be having exacerbation of left-sided heart failure, and may require diuretic medication to reduce fluid overload) for patients who share their observations with their health care providers. Hygiene is the practice of keeping the body clean to prevent infection and illness, and the avoidance of contact with infectious agents. Hygiene practices include bathing, brushing and flossing teeth, washing hands especially before eating, washing food before it is eaten, cleaning food preparation utensils and surfaces before and after preparing meals, and many others. This may help prevent infection and illness. By cleaning the body, dead skin cells are washed away with the germs, reducing their chance of entering the body. Health care is the prevention, treatment, and management of illness and the preservation of mental and physical well being through the services offered by the medical, nursing, and allied health professions.