Whenever I do cambré back (backbend) at the barre, I can't breathe - I have to hold my breath to do it, otherwise, I seem to sink back into my hips. Are you supposed to be able to keep breathing? - It doesn't seem correct that I have to stop!

Yes, you should be able to breathe. A few things to keep in mind:

1) The first movement of a cambre is a vertical lift, the spine lifting away from the hips, the shoulders lifting away from the spine, the head away from the shoulders.

2) When you're completing your cambre, the movement starts with your head/neck/shoulder...NOT the middle of your back. If you do a cambre very slowly the lower back is the last part to move. The movement initiates "from the top" and slowly moves down.

3) Be sure you don't let anything "drop"...everything is always lifted....don't drop your neck (which should be turning your head to the side), don't drop your chest...you have to be your own resistance to leave room for your lungs to expand.

Slow breaths!

AlwaysOnStage, thank you so much for your advice, it is very helpful! Yes, I need to practise lifting while I bend.