My Nephew Became Suddenly Very Sweaty And Clammy With A

my nephew became suddenly very sweaty and clammy with a pounding heart and difficulty breathing. He went to the hospital in an ambulance. His blood pressure was very high (usually normal), but they can't determine what it is. He as a device that he's wearing right now sort of like a pacemaker, but on the outside of his chest. What are the possibilities? (He is seeing the doctor again)