Poor child, poor mama. This is a situation that will probably take some extra effort and care from you and her dad, while he's still home. Anything and everything you can do to help her catch up on sleep is good, whether that is extra story-time before sleep, spending the night beside her bed (make up a bed on the floor for you or her dad), or allowing her to sleep in your room (make up a bed for her on the floor beside your bed).
It's also important not to insist that everything's okay and there's nothing to fear. A terrified child simply won't believe you, and those assurances, though well-meant, will undercut her faith in you. It's better to simply hold her and say something like, "Yes, sweetheart, you feel really afraid right now. I understand. Can you talk to me about what you are feeling?" Sometimes, just that permission to stand in her own fear is enough to allow her to start exploring its dimensions, and limitations.
Another thought: She has gotten seriously jangled by something, and that something COULD be modern chemicals in her diet or in your home. About 25 years ago I went through such a horrible, sudden, unexpected experience of constant panic and complete inability to sleep that I thought I must be dying. After several unbelievably trying months, I gradually learned, with the help of an exceptional doctor, that I was reacting to chemicals. I had become chemically injured (no longer able to detoxify common chemicals in my body), and the resulting irritation to my nervous system was unbearable.
While I was being tested in large groups of patients to find out what I could no longer tolerate, I met a number of children, toddlers to adolescents. It was fascinating to watch them transform from kids who could sit still and color to maniacs who were screaming, bouncing off walls, or huddling in little balls of misery and terror, all within a couple of minutes of having a drop of some dilute chemical squirted under their tongues. The emotional effects can be profound, in addition to skin and breathing symptoms, stomach aches, etc.
If you are fond of modern cleaning products, including fabric softeners (among the worst offenders), air fresheners, and just about any scented product, try bagging these up and putting them in the garage for a couple of weeks and see if your daughter has an easier time (use baking soda and vinegar and unscented detergent in the meantime). Avoid foods with artificial colors, sweeteners, and preservatives.
If there is an improvement, you might want to test by reintroducing some products. Or you might want to skip the toxins and transform your children's habitat into a non-toxic home (google this term for loads of information).
I sure wish you well, and hope you find a quick solution. Your daughter sounds like she's really suffering.