I went 48 Hrs with sleep.I was starting to see giant lizards in the middle of the road, which I was cool with because lizards should be run over if they are in the middle of the road anyway, right???
I did four days once. Like you, I began hallucinating and decided to stop because I worked in a machine shop environment with metal working tools and saws.
But I found it actually got easier to stay awake after day two. Going from day 2 to 3 and then onward to 4 was fairly easy compared to the first 48 hours. It was just the whole not being able to rely on my mind thing that freaked me out. It became difficult to decide what was real and what was not real. I spent a lot of time obsessed with some ants that were getting into my house...
I’m pretty sure I could do longer if I had some time set aside and didn’t have to go to work or drive or anything. But I’ve got better ways to spend my holiday time ;-)
If some researcher wanted to pay me to do it, I’d be happy to accomodate him.