I don't know that there is an exact and precise understanding of what you describe, but what you describe I recgonize as what is loosely called "night sweats". I've had them before. Dating back several years now, I remember they seemed to come out of nowhere, last a while, perhaps a few nights in a row, then go back to nowhere. I have been unable to find anywhere or anyone who can explain to me what these sweats may be about in any clear terms that are easy to follow and make sense of. What I have found is that there is a whole bunch of potential explanations out there, any one of which may relate to being caused by all kinds of illness, disease, nightmares, and in some cases, if none of these apply, the causes can also be grouped loosley into what is called "just a quirk". This leads me to at least lean in the direction of believing there is no single solitary cause but probably is moreso all kinds of different, separate, distinct possible causes. It sticks in my mind that night sweats is on the wide list of the potential hidden effects from mercury poisoning.
Our lives are surrounded with tons of mysteries. This may be an example of one. In the mean time, unless you know of specific reasons to be overly concerned, try not to get too worried about this, if for no other reasons than because it is widely beleived that a person's worries and stresses themselves can provide a kind of feedback into the person that makes whatever problems they have worse. As far as this goes, can you think of any more details about your situation that might play into this?; recent health problems?; illness?; stresses?; anxiety?. Good luck.