I hate this point - especially if it's during a warm-up for a race. The point in time where your body is telling you "ummm maybe you shouldn't do this today."
I hit this point on Saturday, towards the end of my warm-up for the 300m, when I was doing sprints on the corner (typical to do during a warm up for a race that involves one or more corners of the track). One of my hamstrings just wasn't feeling right, and hamstrings are delicate...
So - based on where the discomfort was (at the insertion point with the glute - as in, really high up in the hamstring), I went to my coach and let him know the situation. I knew the risk of injury from racing with the hamstring tightness I was feeling was high-risk, and I didn't want to "make a permanent decision [based on my] temporary emotion." So I didn't. But damn, it was hard. I spend so much time and effort training, for such a small racing period, that I am definitely emotionally invested in each race. But the focus for me is outdoors - so I can't take risks during the indoor competitive season. So I made the right, but hard, decision, and walked away. Literally.
I got some treatment afterwards and iced, and the therapist confirmed that I made the right decision. I did a recovery workout yesterday, and then only upper body in the weight room. This morning I saw my chiropractor (I don't even want to think about how much time I've spent in that office already this year, even though it's only week 3 of 2013), got some acupuncture and did another recovery workout today, and iced afterwards again. So far so good, but I haven't pushed my hamstring since the "no-go". Plan of action is to rest up, and see how it is on Thursday, at which point my coach and I will make the decision whether or not I can race at McGill on Saturday. *Fingers crossed!*