I believe that you have burst eye vessel. It sounds very serious but it isn’t that scary. The causes of this condition are various. Sometimes combination of stress and high blood pressure is enough to get you burst eye vessel.
And sometimes, no matter what you do normal bodily functions such as excessive sneezing and coughing can be a cause as well. So if you can remember what you have done before you lay down to sleep maybe you will find cause of your condition.
The only thing you can do to prevent this happening in the future is to increase intake of vitamin C and grapes seeds because they strengthen walls of the small vessels. Good luck with your doctor and keep us posted.