Yes, that happens to me sometimes. These days, I run about 2.25 miles, preceeded by a warm up walk and followed by a past paced walk (all on treadmill). Every once in a while I have a day like that - I actually always finish my preset quoata (because I don't allow myself to quit) but it's a HUUUGE struggle. On other days, I get into a zone and I am thinking of various things, and the time just flies by.
But, I also call a "bad run" a run when I have to get off the treadmill because bowel movement is knocking on the door and cannot be put off any longer.
I really annoys me to get off the treadmill when I am in the middle but ya know .... what can one do.