Yes, its dangerous. I once did a 400+k bike ride, and after ~350k (18 hours after starting) I fell asleep for just a couple of seconds. Waking up halfway across

Yes, its dangerous. I once did a 400+k bike ride, and after ~350k (18 hours after starting) I fell asleep for just a couple of seconds. Waking up halfway across the road (middle of the night - no traffic) was quite the eye opener. Had I leaned the other way I would have ended up in the ditch.. I was very alert for the remaining few hours, and never felt the need to do another such ride. Of course, running has less risks than biking. But still, falling while running could have real bad consequences.