Many moons ago when I first had my class one I received a phone call from a worried sounding doctor saying there was a problem with my EEG reading. I had to return for a sleep deprived test and all was perfect - as mentioned not eating doesn't help, and movement of jaw muscles etc can affect the reading I was told. You really do have to relax though which i know is easier said than done, but i was so knackered i almost fell asleep which is what they were looking for apparently!?