Good day i experienced couple of weeks ago i started to sweat that my whole shirt was wet.and almost fainted. it happened before last year?

More info ?: Difficult to say. Many things can give you those symptoms. If it only happens once a year and happens randomly it will be very hard to diagnose. Need more info : anything similar between the two times it happened ? Did it resolve spontaneously or did you take or do something ? Etc ?

Low blood pressure?: I would guess that the sweating is not the cause of this problem, but that sweating and nearly fainting are symptoms of something else, such as low blood pressure, hypoglycemia (low blood sugar if you're diabetic on insulin), or heart rhythm problem. How serious this is depends on the cause, how long it lasts, drugs you're taking, and many other factors. See a doctor. Good luck!