Iam a little unfit, but go to the gym 2 - 3 times a week, i dont excesssivley do it but i like to work up a bit of a sweat, iam overweight and do have a poor diet, iam 29, when iam usually training (cardio) my heart rate is quite high (150 - 175) but yesterday it went from 160 which is high down to 72, which is a big drop, i started to feel a bit lightheaded which scared me, please can someone advise me on what to do as am scared of going back to the gym incase i go back and end up having a heart attack or something........or how what can i do if this happens again.....thanks