Sudden sharp pain on my left shoulder blade when going down stairs. cant sit, only standing helps. pain increases with deep breath. rhomboid spasm?

Muscle spasm: Pain like this certainly can be due to spasm in your rhomboid/upper back area. If you have already tried an anti-inflammatory and applied ice/heat to the area without much relief, however, it's advisable you see a doctor to have this evaluated further. Sometimes pain from organs in your upper abdomen can refer to your shoulder blade - such as due to a stomach or pancreas issue.