Jo, sorry I wasn't around last night.
Did you do the race? If so how did it go? And what were you doing up at half past 3 the night before a race, when you had a cold?????
Seriously, for future reference, a head cold is ok to run with, anything in the chest - no way. If you were planning to take it easy, or even run/walk you would probably get away with it, although the excitement and being outside rather than tucked up in the warm, might make the cold a bit worse or last a bit longer.
If you are still feeling low now, take some Night Nurse and off to bed with you. And drink plenty of fluids. And phone in sick tomorrow - you don't want to give it to anyone else, do you.