Hello my name is sam,
the eeg wont last long it's totaly painless, they attatch about 20 leads to your head with a glue- then connect it to a box that connects to a computer so it can read your brain patterns eg activity. They may not have told you but you must wash your hair well make sure you have no gell or wax in your hair ok. They want it to be as oil free as possible. No drinks of coffee or coke or tea. Just sleep your normal way unless you have been instructed otherise.
As for the hyperventilation part they ask you to breathe deeply in and out for a few minutes,
the photo stimulation part is where they get a red strobe light and they put it infront of your face and with the computer they make different patterns and sequences of light flash on and off , faster and faster. Throught the hyperventilation stage. You also get asked to keep your eyes shut. And to keep your eyes open in parts.
Thats all its nothing scarey. You will be fine
i have had 3 of them.