The longest I have gone was 54 hours. My eyes hurt and was weary as hell, but otherwise unharmed. I think I recovered in about 12 hours.
Eyes are the first thing to go for me after about 24 hours they just kinda hurt.
Due to late teen insomnia, I started staying up instead of laying motionless for an hour or two getting back up and then going to sleep. I just started staying up. This pattern continued for some time. I finally drifted into a routine of 24 hours awake and then 6 hours sleep. I did that and was very stable for almost two years. The insomnia returned. I became a bit scared and after a few days of melatonin therapy, I fell back into a more normal, 24 hour based routine. Before this experience I had wished to eradicate sleep entirely. I almost never recall dreams, so it seemed like a profound waste of time. I have resigned myself to a mortal routine, though I still have some issues with insomnia, I can mostly sleep on demand now. It is a puzzle why indeed we must sleep. It is just one of life's givens it would seem.

I love to sleep. I am retired and I sleep when I want to. I love that freedom... no clock, no alarm, no wristwatch... I get there when I get there. Do not underestimate the freedom of doing whatever the fuck you want to regardless what academia and science try to brainwash you into doing something else to be according their collected data. I enjoy the land of dreams too.

I've always considered sleeping kind of a 'necessary nuisance'. I have a hard time getting to sleep, even if I've been up for 2 days straight, and once I get to sleep, I don't wake up easily (BIG problem, I can't take sleeping pills because I'll sleep for 24 hrs straight, miss work, get fired, etc...). So have wondered many times about the bodies machanics and need for sleep. Hope they figure it out.

Well, I can tell you from personal experience if you don't sleep for a month and a half or so, you begin to hallucinate. And while that might sound not all that bad, it's really scary as hell. I don't know what they gave me at the hospital to put me to sleep but it set me on fire for 30 minutes and then I slept for a good long while. We settled on a nice combination of a tranquilizer and a sleeping pill along with several other drugs. Then I slept for at least 20 hours a day for 11 days straight.

Your body needs sleep to heal.

In particular, this need to make up lost sleep, which has been seen not just in jellyfish and humans but all across the animal kingdom, is one of the handholds researchers are using to try to get a grip on the bigger problem of sleep. Why we feel the need for sleep is seen by many as key to understanding what it gives us.

Biologists call this need “sleep pressure”: Stay up too late, build up sleep pressure. Feeling drowsy in the evenings? Of course you are—by being awake all day, you’ve been generating sleep pressure! But like “dark matter,” this is a name for something whose nature we do not yet understand. The more time you spend thinking about sleep pressure, the more it seems like a riddle game out of Tolkien: What builds up over the course of wakefulness, and disperses during sleep? Is it a timer? A molecule that accrues every day and needs to be flushed away? What is this metaphorical tally of hours, locked in some chamber of the brain, waiting to be wiped clean every night?
“What is so important that you risk being eaten, not eating yourself, procreation ... for this?”

In other words, asks Yanagisawa, as he reflects in his spare, sunlit office at the institute, “What is the physical substrate of sleepiness?”

Biological research into sleep pressure began more than a century ago. In some of the most famous experiments, a French scientist kept dogs awake for more than 10 days. Then, he siphoned fluid from the animals’ brains, and injected it into the brains of normal, well-rested canines, which promptly fell asleep. There was something in the fluid, accumulating during sleep deprivation, that made the dogs go under. The hunt was on for this ingredient—Morpheus’s little helper, the finger on the light switch. Surely, the identity of this hypnotoxin, as the French researcher called it, would reveal why animals grow drowsy.

In the first half of the 20th century, other researchers began to tape electrodes to the scalps of human subjects, trying to peer within the skull at the sleeping brain. Using electroencephalographs, or EEGs, they discovered that, far from being turned off, the brain has a clear routine during the night’s sleep. As the eyes close and breathing deepens, the tense, furious scribble of the waking mind on the EEG shifts, morphing into the curiously long, loping waves of early sleep. About 35 to 40 minutes in, the metabolism has slowed, the breathing is even, and the sleeper is no longer easy to wake. Then, after a certain amount of time has passed, the brain seems to flip a switch and the waves grow small and tight again: This is rapid eye movement, or REM, sleep, when we dream. (One of the first researchers to study REM found that by watching the movements of the eyes beneath the lids, he could predict when infants would wake—a party trick that fascinated their mothers.) Humans repeat this cycle over and over, finally waking at the end of a bout of REM, minds full of fish with wings and songs whose tunes they can’t remember.

Sleep pressure changes these brain waves. The more sleep-deprived the subject, the bigger the waves during slow-wave sleep, before REM. This phenomenon has been observed in about as many creatures as have been fitted with electrodes and kept awake past their bedtimes, including birds, seals, cats, hamsters, and dolphins.