No knead bread dough looking slimy after a week
Flour readily absorbs water. You might try adding more flour and mixing it bit longer (yes, I know you said no need to knead bread) when you make your next batch, or you can try reducing the water amount you are using.

If you press on the dough and it doesn't push back it and the indentation remains or if it looks like it wants to collapse it is over proofed. If it is too springy it needs more time to proof. 

Other factors:
Temperature can also be a factor (outside, fridge, oven, etc).
Did you change your flour? Mills change their blends seasonally so you may need to adjust or try a different brand/formulation/protein level. I've had better luck with bread flour formulations over all purpose flour.