I get this a lot but I also have what they call 'silent reflux' which means that the acid from my stomach comes up int my throat without any sensation at all. I only realise when I get mild heart burn and then throat spasms. I've had them all day!!! IT can also be a sign of stress. Though you say that you have slime going from your nose, this can often be associated with allergy and thus the slime could be irritating the wall of the throat?
Of course, there could be other obvious things but I'm not a Dr. I am just telling you what I know.
xx