I'm giving blood this Saturday, through my church. I am little worried about 2 things. 1. I am running my first marathon on 11/2 (5 weeks). Although I am just running to finish, I want to feel good when I finish. Should I expect a slower time, or am I just going to feel like crap? 2. My longest run to date has been 18.5 miles. Sunday I am scheduled to run 3:40 which should be at least 20 miles. I then have one more long run on the Oct 12, of about 22 miles before my marathon. Can I afford to/should I skip Sundays long run? Or should I attempt to do it next weekend and then the 22 miler the weekend after that. I won't be able to do it during the week, because I don't have time. Unless I take a day off work. I don't really want to cancel my blood donation, cause its with my church and I'd feel bad.

Any way you can move your 20 miler to Saturday before you donate?

Well, I didn't have time to do a long run before giving blood. My appointment was pretty early. I did manage a semi long run on Friday then a 1hr run just before the appt. Today, I was going to see if maybe I could do about 11 miles, but even that was not happening . Not even a mile into my run, I could already tell this run was really going to suck. It was one of the longest 4 miles I've ever run. On Friday I am off so I think I will try to do my 20 miler then. That will give me about 9 days until the next and last 20+ run. I want to try to do 2hrs tomorrow , hopefully things will be getting back to normal. Thanks for the advice. You all are very right!