Hi, funnily enough I get this too if I've had a particularly heavy night! I open my eyes and I can see a white circle and then it will go. I think it is related to blood sugar levels. If you've drunk a lot then the morning after your blood sugar levels are often quite low, and this can cause the eye to react in strange ways and produce these visual disturbances. I know I will also quite often get an occular migraine after exercise for the same reason.