What Causes Tightness And Wheezing In My Throat At Night?

My throat seems to tighten at night....dr said maybe asthma but it feels more like my throat..i wake up wheezing and then it goes away and comes and goes like that on and off....i was exposed to a chemical 2 1/2 months ago when this cough and tightness started and also my cough taste like sulfur....scared that maybe this is permanent like cancer or something