HI THANKS FOR CHOOSING HEALTH CARE MAGIC, generally,fever wtih chills ,shivering is seen in malaria where the patient gets high fever which drops after some time and the patients starts shivering fever with chills and rigor occurs in urinary tract infection also did you get his urine tested? if all these are ruled out check for hyper and hypoglycaemic conditions by frequently monitoring blood glucose levels which may the cause of shivering check if the shivering is decreasing after taking some food. fluctuations in blood pressure and sudden low bp may lead to sudden fall in temperature,loss of consciousness also. get his bp levels checked hope i answered your query feel free to contact me for further queries thank you