Metatarsal problem and marathons?

Anybody had a stress fracture on one of their metatarsals? How did it feel exactly? (yes I know it hurt!)Is it possible to do this and not be certain that this is what's wrong ie is there any thing similar that could happen. I ask because my physio is not sure (I have had previous sciatica problems) and I have two marathons coming up, New Forest this weekend and then NY in 7 weeks time.
The strange thing is though I'm pretty sore even walking there's nothing sharp and definite and I feel I could run although in some discomfort. I don't want to take a risk and ruin my chances in New York by attempting the New Forest this weekend. I wondered if stress fractures came in degrees of seriousness maybe?

Puffer, I've had 5 foot fractures, the metatarsal one was the least painful and healed in 3 weeks with a heavy adhesive strapping instead of a cast. The problem with stress fractures is that often they cannot be detected under X-ray until the healing process starts and the formation of scar tissue can be seen. Feels like a sharp stabbing pain when it first occurs and then fades to an ever-present throb, sort of like a headache.
I wouldn't run on it, you'll only make it worse and may end up missing out on NY. Good luck

Thanks for replying Sheila Anne, a marathon this weekend is looking increasingly unlikely now but my physio has agreed to let me do a short run to see if I get sharp pain or just a continuation of the aching. The thinking now is that it may be a tenditis thing at the attachment of the peronius brevis -she certainly found sensitivity there yesterday!!