I would be concerned about the 'flashes'. This could be a sign of problems with your Retina or Optical Nerves. Don't want to scare you, but I suggest a visit to your eye doctor for an evaluation. Losing your eyesight is bad enough, but if you're a photographer ...
Other wise, I sometimes think I can see things in my darkroom when everything is off, such as when loading film. That is just in your mind. As mentioned above, good ventilation is important, and, yes, being in total darkness can make some dizzy.
Good luck!