What Causes Recurring Tremors With Flu And Vomiting?

It s my daughter (36 years young): last week she had the shacks badly. she had been sick with the flue and throwing up a lot. Went to the hospital; they figured she was dehydrated, shakes quit by the time we got there. Now same thing, I tested both hands for strength (same), check both feet (same). Gave her a banana and apple juice, didn t help. Shakes quit in about 30 minutes but she very tired, same as before. She did say she has had these episodes before but only for a few minutes (never mentioned it). She does have back problems. Has a hard time sitting in a chair for a long period of time ( I would say 1 to 2 hours). She did take drugs a while back, but has been clean for 7 years.