I get stunned or blackout often?

It is really hard to explain but when I am in the dark and than go out into the light, I get like stunned or blackout completely for a few seconds and feel like I will collapse or crash into something. Idk what it is but I really blackout often even in the mornings I'm walking and than I go into the kitchen and i blackout so idk whats wrong with me. Any advice or ideas on this problem?