My training has really suffered a setback lately.  A couple of weeks ago I managed to strain a hip flexor due to some pretty intense hill training.  I thought it would be better after a layoff during which all I did was cross train on my bike, but it hasn't worked out that way.  A couple of days ago it seemed to be better, so I went for an easy 30-minute jog.  Felt fine at the time, but a little pain came back the next day.  Then today I went out and was really suffering: not the hip especially, but generally having a miserable time.  I came back and did some yoga on the Wii Fit.  Looked pretty relaxing, but I must have pulled that hip flexor again because it hurt afterwards.
There are few creatures more miserable than a runner who can't run, and none that I can think of right now!
But this, too, shall pass ...