Wanted to bring together all the advice from comments scattered over the last few posts.
On the breath
... check your breathing. Make it BIG and fluid.EXHALE your chest away from your legs, taking weight toward your hands and even past them INHALE your hips way over feet away from your hands Try doing this for every breath in each back bend. Eventually, the inhale will carry you up to stand.
...more into the chest! Slow down the breathing. Keep the hands planted until the last one which is the biggie. The rocking isn't just about momentum, it is also going to open your chest more...
... You are bending your head forward prematurely, which brings your center of gravity away from your feet. Push your weight forward with more momentum, and keep your head back until you are finally standing. Engaging the bandhas and activating your legs will enable you to stand easily.
...The effect of waving your head around will be to make you fall on it. Stop : )
... maybe imagine someone sitting on the ground in front of you just barely anchoring your calves with his palms.Or maybe come up to the fingertips on the last bend.