I experienced this problem about 3 weeks ago and it just happened without prior symptoms. Sometimes, I feel like I need to take a deep breath and when I try to do it, it feels like that the air intake is only partial. When I try it for the 2nd time, then it is alright. I have chronic muscle pain at mid-back close to the right of the spine. I can breathe normal (including deep breath) when I am lying on the bed. Sometimes, when the deep breath is unsuccessful, I sometimes feel a slight pain on the top right chest just underneath the collar bone. The deep breath problem doesn't happen all the time. When I am very consicous and tell myself that I need to take a deep breath, then the problem will happen. I don't think I am short of breath as I feel OK when I am exercising. I discussed the problem with my family doctor and just did an X-ray a week ago. The result came back normal. May I ask if this can be symptoms of lung cancer? I am very worried. I asked my family doctor if there is any further test to be done and he ordered a pulmonary test for me that is to be scheduled soon. Can someone please shed some light on this or share similar experience with me? Thank you so much.