Left eye getting filled with blood during meditation

[Silonasor]

I noticed that whenever I could successfully think about nothing during meditation, my left eye would fill with blood and whenever I open my eyes, my right eye would open normally while my left eye would remain mostly shut for about a second before it completely opens up. This never happened when I daydreamed or failed to meditate.

So what is this? Is it blood flow to a brain region of the left hemisphere?