This is long, but I want to help you.  I am glad you are going to have a scan, to rule out anything serious.  Also, I hope you have not broken a rib.  In the meantime, I have an idea of what may be bothering you.  You can take it or leave it, but I've had similar discomfort and thought it was something somber, until I read about muscle injury, and that explained my problem.  I want you to look at your situation a little differently, too.

The way the chest muscles are set up, they all come up and wrap into the arm.  Find a picture of body muscles online.  Anyway, I was doing pushups after a year of rest, and I seriously injured a muscle in my upper arm.  Simultaneously, I began to notice a pain in my lower chest a few inches over from the breast bone.  Finally I read where someone else had similar chest pain, and it was due to him wrenching a muscle in his arm.  I had not put the two together.  A hernia is also possible, which is a problem from muscle strain.  A plane x-ray will reveal anything wrong with your rib, which can be done at any urgent care center.  If it's broke, they will tell you what to do.  But if it is muscle pain, read on.

Pain is an insidious thing and has a domino effect.  The reason you may be depressed is because you are not keeping active or eating right because of the pain, which will block endorphin flow in your body.  Pain alone will depress a person.  Also, if you don't breathe deeply, you will have a panic attack.  In fact, one of the treatments for panic is to count to ten SLOWLY while breathing in very deeply and lettting it out each count, and I'll bet you won't get to ten.  People must relax and open up to let the healing process come through.  Work through the pain.  

Can you rememeber, Dean, if you pulled a muscle in your arm or did some heavy lifting with your arms?  Or did you do something to strain your abdominal area?  Do you now sort of lean over to protect your chest and tummy area?  Make pain your focus and unwind yourself.  If your scan comes up normal, you could then perhaps see a sports injury doctor to help you.  

This may sound stupid, but, I had the same problem not to long ago.  ALL the same symptoms, it ended up that I had "poop" pushing up on my ribs etc.  They put me on a cleanse for 5 days and I felt so much better after that.  I didn't even think I was constipated, I was going but I guess not enough.  I thought that I had some sort of major problem with the way I was feeling.  I was sleeping all the time, my stomach hurt and I couldn't even breathe in without getting a pain in my chest and ribs.  It hurt as far up as my armpit, which the doctor said is normal!  So maybe this will help, maybe not.