What Causes Unconsciousness After Injection Given For Fever?

Hi Doc. My sister has had high fever for two days with a backache and head ache too. She recently travelled from a city with 84 degrees Fahreneit with 84% humidity to a city with temperature of 82 degrees Fahreneit with 60% humidity. Does she have fever due to this change of weather? She also became unconsciousness when the doctor gave her an injection on an empty stomach? Hope she is ok and there is nothing I need to worry about?