I'm having some trouble with my breathingit feels heavy and like I have to really push to take a breath when I'm sitting down. But when I'm lying down, walking, or jogging, it doesn't bother me at all. I had a chest X-ray and a PFT a couple of months ago, and everything was normal. Do you think this could be related to my sitting posture, or is there something else going on? Would love some advice.