Why does my air conditioner and cold water make me cough?

I sit in my bed at night and do crossword puzzles. A lot of times I feel this sort of ache in my esophagus that makes it hard to take a deep breath and then makes me cough. I have central air and keep it at 68. I have also noticed the same symptom when I drink cold water. I've been freaking thinking it is esophagus cancer or something. The symptom only happens in my bedroom when I sit quietly and breathe steady for a couple of hours. Any ideas?