Listening To Your Body

I was 20 minutes into my usual routine on the elliptical trainer when my body found this to say:

What the heck are you up to, you old fool? You've been listless, to say the least, all day. You basically collapsed in the early evening and went tumbling into the land of nod because you desperately needed to catch up on sleep. You even felt tired going up the stairs to the gym. And now you expect to somehow keep going at a reasonable pace for another 20 minutes! Get real. Get off this thing. Stop pretending you're still seventeen.

Some good points there. But I didn't listen and kept going and, somehow, survived. I suppose there's a lesson in this somewhere - it's just that I don't know what it is.