DD had a cold with aches and pains last week. Then she caught a sickness bug that's going around. At the time her pulse rate was 130 - the nurse wasn't overly concerned as she'd recently been sick and been moved to another building. Her pulse was checked the next day and it was 108 despite sickness having stopped. She's 17, slim, eats very well, plays squash 3 times a week and walks approx 80 mins in total a day, so I don't think it's diet or the fact she's not fit. Any thoughts why it's so high in a young person?