I just happend to be looking for info on Rheumatoid(sp?) Arthritis here and ran accross your post.
I have costochondritis as well, I've been having regular flare up since Nov 05. I'm not sure how much your doc told you about it, but as it was described to me is that the ligements/tissues that connect your ribs to your sternum are inflammed (sometimes swollen). For me, anything I do with my upper arms such as making a bed, washing my hair (I have hair to my waist there's alot of it), scrubbing a floor and things similiar can cause it to flare up. The condition for me gets worse with stress. At one point I was sleeping in a recliner sitting up because the pain just from laying down was too much, I can't lay on my back because of my back problems, so it's side of stomach, and both brought me to tears. My pain is in the center of my chest, more on the left than the right, but often on both. It feels like I'm being stabbed in the chest over and over often times. Also, if you press on it at all, it feels like you've punched me and will stay hurting for hours afterwards.
Another thing you haven't mentioned, are you on any anti-inflammitory medications? From what every doctor I've talked to has said anti-inflammitory medications should be your first treatment option. I went from Aleve, to 800mg Ibuprofen, to Naproxen (same as aleve just a stronger dosage), to one I can't remember the name of because it made me sick, to finally Celebrex 200mg once a day. The only one that has made a significant change is the Celebrex, I can actually do things like wash my hair and make the bed withing 6 hours of each other. Another thing, that actually made me pain free from the costo for awhile was I had two steroid injections, one in each hip, and was put on a 7 day steroid dosage pack, the costo didn't bother me for about 2-3 weeks.
As far as when to go to the ER I couldn't tell you. I have yet to go, and there have been times when my husband has been on the verge of forcing me to go. I'm stubborn and dont want to have to pay an ER bill. I would say to "learn" what your costo pain feels like. It's very similar I've been told a heart attack in it's symptoms, BUT I've been told if you get used to what the costo feels like, you'll know if your having a heart attack because it will feel different. I hope that makes sense. I would talk to your doctor about "when it's time to goto the ER". The times I've almost caved in are the times when I can't breathe from it because it hurts to much. These are also the times when I'm in so much pain that I throw up, get chills, sweats, and dizzy from the pain.
I hope soem of this helps :)
"When we come to the edge of the light we know, and are about to step off into the darkness of the unknown, of one thing we can be sure; either God will provide something solid to stand on... or we will be taught to fly.'"
"Cause when push comes to shove You taste what you're made of You might bend, till you break Cause its all you can take On your knees you look up Decide you've had enough You get mad you get strong Wipe your hands shake it off, Then you Stand" From "Stand" by Rascal Flatts
Dx.: Polycystic Ovarian Syndrome, Ulcerlative Colitis, Chronic Inflammation of the Colon, Ruptured & Fused L4-L5-S1 w/pinched nerves, Chronic Costochondritis, Back Muscle Spasms, Asthma, Benign Tremmors (hands)