Anyone else experience dim vision or a shadow across the eye for 2 seconds?

Hi, recently this month i've noticed my vision going dim for like 1-2 seconds. It looked like someone lowered the intensity of light. However, this happened even when i don't turn on the light. Also, i notice this usually when i'm studying. Anyone know what it could be? My appointment to see my eye doctor is in a month and i want to find out earlier if it is serious.