Major temp drop

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Kyle has been sick for a week.  actually he has had a low grade fever (100.4) everyday since last Monday.  Horrible cough, diarrhea started today.  He had a chest xray to rule out pneumonia- negative.  Well, this morning his temp was 103 and he was very lethargic.  We did tylenol and motrin alternating.  He took a 4 hour nap and now his temp 96.  We have taken it with two different thermometers 3 times now.  Any thoughts why it is so low now?  Poor kid!