Can't open my eyes when I wake up due to Rheum (commonly known as "eye gunk/eye boogers")?

The past 2 days I have been not been able to open my eyes right away without having to clean my eyelashes since they stick together. I have been sick since Friday, my doctor told me it was just a virus and to take Advil. Why does this happen when I'm almost all better? Is it because of the extra mucus?