They'll either use a flexible 'helmet' with marked areas to insert the electrodes, or just map them out on your head. The adhesive is a little annoying, so if you have time afterwards, you might want to shampoo your hair. It's generally done on a very relaxing stretcher or bed, and they might flash lights, ask you to breathe fast, have you open and shut your eyes on command, but mostly you just lie there and aren't supposed to move. It takes about 20 minutes to set up, and about 30 minutes to an hour for the readings. If you fall asleep, or doze off, that's fine. IF you can possibly take the day off afterwards, to get your sleep back, it might be better, so you don't set yourself up for any episodes from not sleeping the night before (probably the most annoying part of the test). It's painless, and generally comfortable. I've had them in beds, stretchers, recliners- none were any worse than the other.