It is very unlikely that the Lumia 60k vitamin D tablet is directly causing your chest tightness. Since you are fit and healthy, this sensation is much more likely related to the stress and physical exhaustion stemming from your long-term sleep problems, which can frequently cause muscle tension and chest tightness. However, your comfort and safety are what matter most. I suggest pausing the supplement for now and speaking with your doctor to discuss your sleep issues and rule out any other causes. If the tightness is severe, worsens, or is accompanied by shortness of breath, please seek medical attention right away.