I am so tired

My eyes are burning. I've been working all day and I still have something huge to do before tomorrow and I'm not exactly sure when it's going to get done. I am so tired. But I have another mega-long day ahead of me, followed by 21 more after it, so I don't know if its better to sleep now or plough through and be done. Either way, my mind is drifting and I keep finding myself on websites that are not work related, so I must be trying to tell myself that its time to be done.