The corneas' response to this event varies between no discernable effect to extreme pain and blurred vision.
This can vary between individuals, and with different lens types and can even vary with the same individual on different occasions.
The degree of discomfort depends on the extent that the cornea swells in response to the lack of oxygen. It usually does no permanent harm to the eye, although if you get the painful response you will inevitably end up at the eye hospital convinced that you are going blind!
It is important to remove the lenses on waking. They normally come out without any problem, although sometimes they can dry out and stick to the eye. If this happens, it is advisable to irrigate the eye with sterile saline to re-hydrate them, so that they move again, before removal.
Treatment is normally time, perhaps with some aspirin. Very few people are keen to repeat the experience!
However, if you 'nod off' for a few minutes in front of the TV - you will not do yourself any harm.