I took 4 mg xanax (alprazolam) prescribed , but i'm like really sick and have a fever was wondering if i can take nyquil to help with the fever and sickness?

Large dose: the largest alprazolam (xanax) tablet is 2 mg, and that is already a high dose, so I don't know exactly what you are taking, or why it was prescribed. Xanax is generally given initially as 0.5 or even 0.25 mg three or four times daily, and a common dose might be 1 mg three times a day. NyQuill is meant for cough, and to treat fever aspirin, acetaminophen or motrin works best & is ok with xanax.