It's not gross.
It doesn't affect me apart from makes me feel a bit more lightheaded than usual (I suffer from hypotension, or is it hypertension LOL I can never remember. Low blood pressure anyway which makes me sometimes feel dizzy). Other than that, no, no problem. However everyone's different aren't they, so if it does affect you, just take rest days, or swim or something - whatever you can do.
Paula set the world marathon record at Chicago after waking up that morning to find that she come on early. She said it was hardly ideal but just went out and saw what happened. ;-)