When reading a book or looking at my computer, my vision becomes cloudy and black. should i be worried?

Maybe: The blackness should be differentiated from blurring. True blackness is a different problem and should be addressed immediately. The blur is usually caused by glasses or dry eyes. These are usually easy to remedy by on ophthalmologist.

See an eye doctor: It is not uncommon for vision to blur when reading or staring at a computer for a long time. It is less common to have vision black out when performing these tasks. See an eye doctor soon to evaluate the cause of the diminished vision.