At first, he thought it might be an optical illusion, a mere trick of light rays, but the more he looked at it, the surer he became that there was a second moon with solid outlines up there. His mind went blank as he stared in its direction, open-mouthed. What am I seeing?
(H. Murakami; 1Q84)
Do you often use 'see' in the present continuous in this meaning?
What am I seeing?
Where am I going?
What am I doing?
What was I thinking?
These are all frequently used present continuous expressions.
They may start within one's mind, but could be expressed either silently or out loud.