I've noticed after running that sometimes I'm on a high, other times I can feel quite down and gloomy. This has never happened to me before, I always feel up after any exercise. I've noticed the times I feel up are the times I've pushed it a little, for example when I've done the C25k+ podcasts. I'm wondering if this is to do with heart rate, maybe I'm kinda in the wrong zone with my slow distance running... I don't have a heart rate monitor, I usually take my pulse at the end of a length when swimming with that big clock! Anyone got any info on this?