Annoying Night Sweats

Because of this, I researched about it and this is what I found in the internet:
(Source: http://aids.about.com/od/otherconditions/a/nightsweats.htm)
We all perspire. In fact the average person losses about 1 quart of fluid a day by sweating. But for those living with HIV, night sweats can be a very annoying problem. What are night sweats? Why do they occur and what can be done about them?