One awful run in the course of many is to be expected. Sometimes though, endorphins behave unexpectedly...

'Endorphins may also be responsible for heightened states of rage or anxiety. If your endorphins overdo their job or the hypothalamus misreads the endorphin cue, you could be flooded with "fight-or-flight" hormones at the slightest hint of trouble or worry.'

It seems like maybe the chemical release of the run could be working against you today. Sit and breathe. Drink lots of water. Eat a grounding meal. Punch a pillow. Let it pass.

Runs can be pleasurable again. Try not to worry. No need to jump to conclusions yet. Hang in there.