Sore or Injured

I mentioned yesterday that I was sore from doing that crazy-cool lesson over and over. Well, it looks like it's more than just sore. I went to bed with a heating pad on my inner shoulder and when I woke up this morning and tried to move it I was in pain. I thought, "crap, I injured it!" It got better throughout the day and now it just feels sore again. So what's the differrence between sore and painful and injured? I guess it's a matter of degree. It hurts more than last night but a lot less than it did this morning. My range of motion and ability to lift with that arm is a bit limited. I wonder what tomorrow will bring?