For a dancer, realizing she can't dance (whether it's on her own or being told by a teacher or doctor) is morally and emotionally crushing. Sitting out of class seems nice at first (finally get to rest), but your heart and soul want to dance! Your body just isn't into it.
For the past 3 years, I've dealt with injury after injury: foot (cuboid), knee, back, foot (cuboid again), back (vertebrae), foot (navicular), back. I suppose I'm lucky that none of these injuries have put me in crutches or casts and that I've largely been able to function on my own, but many of them have taken me out of class for significant periods of time.
I'm writing this because I've been struggling with a twisted vertebrae (which is pulling 9 others out of place with it) since October. It took me out of class for a month and a half and I'm still adjusting. And just today during class, I felt something in my lower back go. I'm currently dealing with low back pain with which I can't walk or sit without feeling.
So what do you do when you have an excruciating injury? Ice/heat, roll it, stretch, or rest. Talk to your teacher. Talk to a doctor. Talk to friends, physical therapists, parents. Anyone who will listen, you tell and get advice from, hoping something will fix it. Opinion after opinion and you realize that you're just going to have to live with it for a while.
And that's when you start to give up. Exercising releases endorphins, which you're not getting anymore. Your brain and body are used to those endorphins. Dance is your life, and it's something you can't do right now. All you want when you're tired and dancing is to sit out and watch, but when you're injured and watching, all you want is to dance. Desperation, mild depression, and frustration settle in because there's little you can do but wait. We've all been there.
All I can offer is to cry. Cry with someone who will listen and get it all out from time to time. Write if that's your method of getting it out. You need some way of releasing the tension and frustration that isn't dancing (usually how dancers release tension...) because you can't dance. If you let the frustration and negative energy sit and build in your body, it will take even longer for you to heal.