When she has her head down, she's relaxed and comfortable and being submissive. She could also be stretching her back as well, if she has found that it feels good. :)
The head high and being tossed about could just mean she's feeling good and her energy level is up. I wouldn't say it's disrespectful, but in those times you can just quietly reel her in on a smaller circle to re-focus her attention back on you.
If your mare is light and sensitive, a verbal cue might be enough. For the more lazy/ignorant/uneducated/stubborn type horse, you can use another means to get the response you're looking for. It's a series of progression, really. Kind of like the "goldilocks theory". Start with a little, then add if necessary. I cluck/kiss, then if nothing I'll raise the whip, and if I have to I'll tap the haunches or the hind leg to ask for an upward transition. Or flick the tail of the whip on the ground at their hind end. What you want is to teach your horse to listen to verbal commands, or something subtle. Teach your horse that when you whisper to her, she hears you. If she doesn't respond to something small, you have to do something bigger. The next time she will remember the repercussion of not listening to the subtle cue, and will choose to respond off very little.
You can be in various positions while lunging, depending on your level of education. If your horse tends to lean in with his shoulder, to aim for the shoulder and up towards his throat. If he says perfectly in balance, you can remain a bit more at his barrel. If he tends to get crooked and wants to bulge his hind end to the inside, you can position yourself a little towards the back so that you can push his hind quarters out and drive him forwards. Alot of people say that eye communication is important, I however don't think so. They say wild horses will stare another in the eye if trying to gain respect, or if they are trying to drive that horse away. In lunging, it's more about your body communication and the energy you reflect. If you have alot of bounce in your step, or alot of energy in your cues, your horse will respond quicker and with more life. If you are slow, non chalant, calm, you're horse can mirror that energy as well.
If you want your horse to move forward, walk at him in a manner that you want to drive him out and forward. Continue walking with him in a smaller circle, and when you want him to slow down or either stop, you stop walking, or you take a step backwards. That relieves the pressure of you driving him out, and he will relax and slow down. Always send from the back to the front.
To ask for a halt, stand quietly in the center, calm and peaceful. Hum to him to whoa, if he doesn't respond you can reel him in closer, or just gently pull the lunge line until he responds. Alot of horses will stop and face you. Some people don't like that, others it doesn't matter. You can teach your horse to halt straight by every time he comes to turn into you, you just push him back out and give him a place of peace when he's facing forwards again. It's not a bad thing, really. It's just that he's checking in with you, wondering if he has done a good job. :)
You can watch her footfall to tell if they're tracking up. Does the hind end hoof print fall in the front foot's print? Or does it fall short, or does it exceed the front? If the hind print doesn't reach the front, he's not tracking up. Bring him in on a smaller circle to where you can touch his hind leg with the end of your whip. Touch his inside hind leg just as it's about to leave the ground. This will encourage him to reach further with his leg. You can repeat however much you want, but make sure to give him a place of peace when you see an effort on his part to reach farther. You can do this also to ask for trot. Tap the hind leg a little harder(if your horse tolerates it) until he responds and pick up trot. This will encourage him to push himself into trot from his hind end. Alot of horses do not have awareness of their whole body. Tapping their hind legs brings awareness, which improves better movement and a calmer, happier horse.
I do alot of long lining, which is a bit different from lunging.
That is pretty advanced, but I just wanted to show you what you can do. You have the inside rein, and the outside rein. So basically you're riding them from the ground. You are able to be way more effective and can fix and cause things easier. :)
Hope this helped you, there's def. Alot to it!!!