Dear Friend, Besides the opinion my doctor friend has expressed, I think you might be having episodes of epilesy, I suggest you get  a plain CT scan and EEG done and see a neurologist before the problem becomes worst. I wish you a happy and healthy life. Regards Dr. Anamay Kamalakar Bdiwai Chennai

hello der if you are getting unconscious after walking or standing for long time its due to pooling of blood into lower limbs.....as a result brain gets less blood supply...hence in order to increase the supply brain perform this action and it may be due to postural hypotension or symathetic system failure consult physician for further evaluation and treatment.