It's not just vision that's bad - we tend to hear and feel things less well for a few seconds on awakening. Possibly, there is also a need for readjustment of the focal length of the lens of the eye, which relaxes in sleep. The cones enable us to see in bright light and is responsible for colour vision.
Night vision is only possible if there are certain pigments present in the rods.
These pigments are constantly being formed by the eye and are inactivated by light. Hence when you walk into a dark cinema, your eyes take some time to adjust as they need the time to form the pigments. This holds true also when one wakes up in the night as the eyes will need time to adjust. This is normal. However if your night vision is constantly poor, it may be a sign of vitamin A deficiency as vitamin A is needed to form these pigments.