I seem to have a problem with my heart rate going through the roof during the first couple of games of a singles match. During change-overs I notice my heart is pounding away and won't subside until later in the set unless the match is a grinder. I think it's partially because I'm not in tip-top shape, but also because I overreact and try too hard. I react to everything with explosive movements, rather than just relaxing and breathing. Any tips for bringing the heart rate down both mentally and physically?