I believe parenting classes can be really helpful in a case such as this.
I would search for "positive discipline" type classes in your area. If you're having difficulty finding any, then I would search for family therapists who have a clinic (not a single office), with multiple therapists / doctors and give them a call and ask where you could take some classes.
When something starts out of the "blue" like this, I think you have a right to be concerned.
Maybe something happened - an incident that has made your daughter not want to be alone? Is there anything you can think of? Has she gone away / slept away from you this summer? Has anything changed - or will be changing soon that she knows about?
Sometimes its difficult to figure out what drives a sudden change of behavior. Have you gently sat down with your daughter and talked to her about her feelings / being scared?
Does she seem "typical" in the day time? Any red flags there?
From a Mom who has a very challenging daughter, I understand your concerns.
It is hard to say without knowing your daughter, but from your post, right off the bat I think "anxiety". Anxiety about learning something new, anxiety about doing something out of her norm, and with some guided pressure from you, the stress that she perceives, turns into a meltdown.
Something as simple as taking tablets (which she successfully did before), may seem easy to you, can provoke stress in those children who are susceptible.
My thoughts would be to find a Dr. who can assess your daughter, listen to your concerns, talk with your daughter, and recommend treatment that would help her learn to cope with tasks she is unfamiliar with in a healthy way.
Well, if I were you I would not wait. This is your child, and you want him to feel better, and more connected at school.
Waiting is doing nothing, and a more involved parent is always a good thing. You are your son's voice and while he is still so young, you have a right to always talk with his teacher and get involved when your son isn't feeling right.
I think a face-to-face with the teacher is an important step.