Hello! Thank you for asking on HCM! His symptoms seem to be related to an infection. I would like to explain to you that infection and high body temperature are usually associated with tachycardia, as a response of the heart to this condition. Have you measured his body temperature? Did he have any complains during being overheated in the tube, or before sleeping? A heat stroke would cause immediate symptoms during overheating and not after sleeping for some hours. I recommend you to consult with the pediatrician, and perform a careful physical examination, routine blood tests,an urine analysis, chest x ray. Further tests may be needed to establish the cause. Hope to have been helpful! Greetings! Dr. Iliri