Breathlessness at night. Of all this?

I feel breathlessness feeling at late night in middle of my sleep. I start coughing a lot continuously and feel difficulty in breathing for half and hour or so and then it becomes completely normal and I can sleep again. There is a whistling sound from my nose when I'm breathing during this period. This happens regularly at night. People around me have told me that I snore at night during sleep which gets intensely louder and is broken by coughing and me waking up. I had visited a general physician with this issue and I was prescribed tablets to crush and inhale everyday for a month. I didn't feel any  problems while taking the tablets but now I'm feeling it again. What should be my course of action? Should I visit a chest specialist? What could be the cause of all this?