Brief Answer: Normal autonomic reaponse sir Detailed Answer: Hello sir and welcome. Thank you for writing to us. I should rightfully start by saying that this is most probably a normal response. A part of the brain (i.e. the autonomic nervous system) controls the emptying of both the bladder and the digestive system. But it has various other functions as well, out of which one is the control of the temperature regulating region of the brain. When this part of the nervous system sends out a response yo empty the bladder or the digestive tract, it gets hyper-stimulated which results on messages being sent out to other regions of the brain that it controls as well. This results in the stimulation of the temperature regulating region during or immediately after urination or defecation, resulting in the shiver either only in the head region, or at times from head to toe. Unless you have other symptoms like numbness or pain in the genital region, or light headedness or loss of consciousness during or after urinating or defecating, there is absolutely nothing to worry about. I hope you find my response both helpful and informative. Please feel free to write back to me for any further clarifications, I would be more than happy to help. Best wishes.