Hi Julia,
I'm sorry to hear of your pain. I thought I should get in touch as I have experienced this. My short history with costochondritis is that I've had it for 8 years now, since I was 16, and it's coming up for 2 years where I've had it with a vengeance. I'm a Latin and ballroom dancer so I understand what you mean about pain when dancing, sometime I just have to stop.
if it helps, I can share with you a few things I have found help with costochondritis?
1) Exercise can help some people and hinder others.
i have found myself if I leave off exercise as a whole (as most health sites suggest) I get stiffer and the pain gets worse. Gentle exercise works quite well, stopping when I feel sharpness. I have just taken up Pilates once a week and whilst is isn't reducing pain, it is helping me to stay mobile.
2) Don't panic, just stop.
Its hard not to panic so this may sound like a silly one, but over time now I guess I've come to expect the pain which makes it a little easier. Sometimes lifting shopping bags gives the strongest of pains and I've just had to drop the bags (even though I smash the eggs!) So just stop if you need to. I'd also recommend Pilates for this as it does help you to stay calm and for me it's a nice group of friendly faces who understand pain when moving, even though it's usually back pain for them.
3) Gently warm up before dancing
I've found gradual warm ups that work through the shoulder area and then side leans can sometimes help before dancing to loosen up.
4) Voltarol
Have you heard of this? It's a gel form of diclofenic available over the counter. For me, it doesn't get rid of the pain, but when particularly painful and struggling to breathe I find it can reduce the sharpness. So I sometimes use this when dancing.
I really hope this helps. If you have any questions, I'm here and I'll keep checking back.
Can I ask, what kind of dancing do you do? How long have you had costochondritis? Have you ever had your heart checked to rules to it out? Do you have any clues for what might have caused your costo? (I'm afraid I know of no cause for mine, some people's are caused by trauma though and the general advice here is to rest and avoid exercise.)
Costo pain traditionally happens across the chest, but often is accented across the left-hand side because there's more in that at side - more pressure and more tender cartilage.
looking forward to hearing from you,
Adele