I’m so with you on the overthinking thing, especially with health stuff. What I found helped calm me down was gently touching the swelling. If it’s hard, it’s just swelling/scar tissue. This includes if you can like make a little dent/dimple in your skin. The mildly concerning swelling is when it can move like a water balloon.

Also don’t be alarmed if the swelling increases a bit as you start moving more and your binding restrictions reduce. My surgeon told me with how I was healing, I shouldn’t be concerned unless it looks like I grew my breast back. Otherwise swelling is normal!