I took A&P 1 and Micro this summer (3 days/wk, 9 wks) after returning for my second degree (graduated in '05).
While it is not the easiest thing to do, if you have no choice then you just do it. I was stressed before it even started! What if I fail, i haven't done this in 5 yrs and i have 2 hard classes, etc...Basically, my husband layed it down and explained I didn't have a choice, I HAD to do it.
And guess what?! I made 2 A's!!!!
So, if this is what you really want and you have to then do it! If not, then wait.