For the last couple of years I've taken to 40 mins of power walking in the evening after work. I was seriously unfit (although not overweight). The walking is OK but sometimes I've tried to jog 40 yards, then I also feel as though I'm going to have a heart attack and by the time I'm home I have a sparkly thing going on in the corner of one eye, feel drugged and just blob on the sofa! I then worry I've overdone it but I am still here. I think I'm just in tune with my nerves ;-) Maybe you are too.