I have candida overgrowth and I used to get the same thing (didn't know the medical name though). While I avoid anything medical or pharmacutical in fighting the candida, there is actually a great prescription anti-fungal ointment that will kill that painful flairup within hours. It's called Lotrisone. Natural antifungals might work but I think this is likely more immediate. Keep in mind that the reason this is happening is that your candida has gone systemic (i.e. throughout your body) and is plentiful in your saliva. When you sleep you drool a bit (yes we all do!) and it's that fungus from your saliva that causes the cracking in the corners of your mouth. Though I haven't beat my candida yet, I never get the cracking any more because I oil pull, which very effectively detoxes the mouth (and hopefully the body by entension). I highly recommend oil pulling for anyone with candida.