The fainting spell could have something to do with the cleanse (detoxing), or nothing to do with it. Either way, you'd probably be fine if you chose to soldier on through. However, if you don't feel it's right for you now and choose to break, there's no harm in that - just be sure that you break properly, per the directions in The Master Cleanse book. Otherwise, you could get sick or feel really awful.
As far as I know, that would be the only bad side effect of stopping before the 10 days.