Because you're normal. Most of the answers here are straight up crazy.

You can adopt a polyphasic/biphasic sleep schedule, although less research has been conducted on that method. Uninterrupted sleep is better in theory.

In response to everyone who claims that they "don't need" 6 hours of sleep:

You may feel fine now, and you may feel fine in 5 years. But you will not feel fine later on in life when things catch up to you. It isn't healthy to get under 6 hours of sleep, no matter what you "think" you can handle/need. 

It is normal in today's world for a large portion of the population to get 5 hours of sleep. But just because something is normal, doesn't mean something is healthy. I would suggest trying to achieve AT LEAST 6 hours of sleep per night. Even though 6 - 6 1/2 hours can be just as unhealthy for some people. Optimally you would want to get 7-8, but that isn't realistic due to tight schedules/life/etc. 

I'd say 8.5 hours seems like the sweet spot for having just enough sleep to not accumulate any sleep debt. About 7 hours is fine for some time, although I don't exactly like it, and for really short periods, even 6 hours goes. Anything below that, and sure, I can function, but it sure doesn't feel like that.

If I get 5 hours, I'm lucky.

You almost certainly have a sleep related disorder, and should seek to get a sleep study if possible. Either that, or you have terrible sleep hygiene. Just looking into a sleep study wouldn't hurt though. It can reveal a lot of helpful information to augment/repair your sleep issues.

This may be a problem related to sleep hygiene or environmental factors preventing sleep. Although in many cases a problem like yours can also be respiratory issues preventing continuous sleep. Respiratory issues such as sleep apnea are very common and deadly when left untreated.

Risk of stroke and heart attack rise significantly. There are arguments supporting the theory that Obstructive Sleep Apnea (OSA) is more harmful than cigarette smoking. Looking in to a sleep study could be very beneficial for you. 

I don't like diet coke ^__^

All I need is three to four on a regular basis. I do require a good eight hours, roughly, every two weeks. In essence, I am able to stay up for long periods of time without sleep so long as I don't lay down. That does, however, shortens the period of my need to recharge at eight.

I can also reach REM almost as soon as fall right to sleep. That's how I can easily refresh on a fifteen minute break at work.

There is downside to this I ran into... but I am not going to reveal that part. Fuck that.

4 to 8 hours of sleep.

Since you reach REM soon after you fall asleep, I can almost say with certainty you are sleep deprived and doing damage to your brain.

"REM rebound" is the main indicator for regular sleep deprivation. 

That's a pretty large disparity!