Sudden blurred vision in both eyes

I woke up one morning and suddenly realised that I cannot see distant objects clearly. This was a few days back. I went to the doctor and he confirmed that my vision has increased by -1.5 in each eye. He could not find anything wrong with my eyes - it was very dry, but apart from that there was nothing wrong. I don't have any symptoms other than blurriness in both eyes. Surprisingly, the blurriness of vision happens when I wear my glasses. When I wear my contact lenses, my vision improves to almost normal. I know there is nothing wrong with my glasses - I have 2 pairs with which I could see perfectly well till the onset of blurred vision the other day.
This is the second occurance of blurred vision for me. A few months back, I had conjunctivitis which they treated with steroid drops - the blurriness of vision followed. The blurriness lasted 1-2 weeks and went away on its own. I went to 3-4 doctors last time and nobody had an answer for what caused the blurred vision.

Here is what I want to know:
1. Is there any disease/condition that can cause sudden onset of blurry vision in both eyes (other than diabetes which I don't have) ? (I think I am reasonably healthy except for the blurred vision)
2. Is there any eye condition which could cause blurry vision without eye pain or any other symptoms? Could dryness of eyes lead to such a drastic vision change? Or could it be that my eye muscles are weak?
3. Is there any cure for this?