Agreed. Pure agony. Afterwards I am so exhausted that I often find myself at the edge of tears. Worse it seems to turn off my immune system and I often get sick

Agreed. Pure agony. Afterwards I am so exhausted that I often find myself at the edge of tears. Worse it seems to turn off my immune system and I often get sick. But I do have a clearer head for a few hours after a run so I keep doing it.