I was playing Dragon age origins all of yesterday and the day before. I got the worsed headache I've had in a long time just before I went to bed. I was convinced I had consumed some dangerous food colouring or eaten something bad. After rolling in pain until 6 am I decided to look on the internet for others who had headaches after long gameplay sessions. 
 
To my horror I realised that this was a common condition for gamers called "eye strain" which causes headaches. After all the warnings I received about playing games and having breaks. I thought this would never happen to me! The night was hard and I have resisted the urge to play more games today. If you read this take breaks every four hours for at least 15 minutes. You do not want the headache I had last night.