How to stick out marathon sessions and play close to your peak

[Teh1337zor]

Occasionally I will get in a game that I feel is just too good to leave, I sat playing for 16 hours and ended up up around 5 buyins. However towards the end I felt my game got a lot duller and I wasnt thinking things through. How do you keep focus in long sessions like this and what techniques do yoou use to stay more alert