For the last week or so, I’ve had chest pressure/tightness on my left side. I mostly feel it when I completely exhale. No other symptoms, haven’t been sick in well over a year and healthy. But it’s freaking me out since I get health anxiety. This happened to my sister once and the doctor said she pulled a muscle in her back, which was restricting her rib cage. My mind goes to Pulmonary embolism or some type of clot every single time though. There is no pain, thankfully. 

When I stretch, I feel the pressure/tightness less, so it leads me to believe poor posture and anxiety or something has led to pulled muscles. I’ve had a stressful last couple of weeks. This ever happen to anyone else?