The text does not tell too many specifics about Betty Parris's "illness" and her symptoms. What is definitely told to the audience is that Betty has not moved herself since midnight. Even somebody that is asleep tends to move in some way. Symptomatically, Betty seems to be in a coma like state. She breathes, but in no other way does she respond to the environment around her.
The only other key detail that the reader is given about Betty is that her eyes are closed. That may seem obvious, but it surprises the Putnams, when they come to visit. Mrs. Putnam says that her daughter, Ruth, has the same lack of response as Betty. The difference though is that Ruth's "coma" seems to be an awake coma. Her eyes are open, and she walks around; however, she doesn't respond to anything.
Mrs. Putnam: She ails as she must - she never waked this morning, but her eyes open and she walks, and hears naught, sees naught, and cannot eat. Her soul is taken, surely.