Navy SEAL Hell Week is a five-and-a-half day stretch in which candidates sleep only about four total hours, run more than 200 miles and do physical training for more than 20 hours per day.
Navy SEALs go on missions to raid, ambush and assault enemy forces or terrorist cells. These missions include a lot of sleep deprivation. So in training during Hell Week, as it’s called, Navy SEAL candidates must stay awake for five days in a row to see if they can handle it.
4-mile run in 31 minutes
SEAL candidates begin training with a two-month course at the Naval Special Warfare Preparatory School in Great Lakes, Illinois. This is called Stage 1. The Official Naval Special Warfare Website explains what a candidate must be able to do after the course: 
The two-month training period begins with a Physical Screening Test. The goal: Improve the candidates’ physical readiness for the rigorous activity they will face at BUD/S.
The Prep School ends with a modified Physical Screening Test. The test is a 1000 – yard swim, push-ups, pull-ups, sit-ups, and a four-mile run.
The minimum standards for this expanded test are as follows:
1000-yard swim – with fins (20 minutes or under)
Push-ups: at least 70 (two-minute time limit)
Pull-ups: at least 10 (two-minute time limit)
Curl-ups: at least 60 (two-minute time limit)
Four-mile run – with shoes + pants (31 minutes or under)
Candidates who don’t pass the longer, more intense test are removed from training and reclassified to other jobs in the Navy.
I bet those who flunk are thankful they don’t have to do the sleep-deprivation. That doesn’t come until Stage 3, several weeks later.
Stage 2 introduces the recruits to the special operations lifestyle and lasts three weeks.
Stage 3, First Phase, Basic Conditioning … let the SWCC site explain it:
First Phase, the basic conditioning phase, is seven weeks long and develops the class in physical training, water competency and mental tenacity while continuing to build teamwork. Each week, the class is expected to do more running, swimming and calisthenics than the week before, and each man’s performance is measured by a four-mile timed run, a timed obstacle course, and a two-mile timed swim.
Because of its particularly challenging requirements, many candidates begin questioning their decision to come to BUD/S during the First Phase, with a significant number deciding to Drop on Request (DOR).
Hell Week: 5 days and nights without sleep
The next part of training is known as Hell Week. In this grueling five-and-a-half day stretch, each candidate sleeps only about four total hours but runs more than 200 miles and does physical training for more than 20 hours per day. Successful completion of Hell Week truly defines those candidates who have the commitment and dedication required of a SEAL. Hell Week is the ultimate test of a man’s will and the class’s teamwork.
The next phases include combat diving, land warfare training and finally mastery of SEAL skills, which includes the infamous SERE training—survival, evasion, resistance, escape.
No wonder only about 25 percent of people who enter the SEAL program graduate.
Falling asleep standing
Brad MacLeod, former NAVY Seal and founder of the website SEALgrinderPT.com gives the reasoning for depriving these young recruits of sleep.
The BUD/S trainees stay awake for five plus days in Hell Week to make sure they can do it in a war zone. SEAL operators and war veterans often have had to stay awake for 72 hours on and 12 hours off shifts. When a battle breaks out you have no choice but to stay awake and get the job done.
(BUD/S stands for Basic Underwater Demolitions/SEAL.)
If they make it as SEALs, that’s just the beginning. For their entire career, they have to go on missions during which they don’t get much sleep at all.
He said he found consuming caffeine doesn’t do much, except drinking coffee or tea helps to keep warm. But he added that some SEALs put the instant coffee in their pre-packaged meals in their cheek like a wad of chewing tobacco.
His No. 1 tip to stay awake? Keep moving.
“That is the first rule. If you stop moving you will fall asleep. Doesn’t matter if you’re standing up or laying down. You will fall asleep. Keep moving.”
The TRUTH about sleep deprivation
According to Medical News Today, sleep loss “alters the normal functioning of attention and disrupts the ability to focus on environmental sensory input.”  This may explain why some Navy SEALs in training experience hallucinations, like below: 
Due to it being Thursday night and my euphoria setting in heavily, I mistook one of the students swimming up in his black dive mask and wet suit as a seal and remember getting spooked, yelling and pulling my paddle in to protect myself, nearly hitting him in the face.
The guy paddling behind me had to grab my arm and say “dude, it’s cool, stop!” I then realized what was going on and became incredibly thankful for the McDonalds Cheeseburgers that had just been tossed into our boat. Again during another leg of Around the World, I thought a dead tree on the bank of San Diego Bay was moving and told my boat crew to watch out and that it was coming right for us!
This was about two hours before I was in the number 1 position at the front of the boat, calling the stroke count out loud (to ensure everyone was paddling the same) and fell asleep and into the water mid-sentence.
Sleep deprivation symptoms
So what happens when you lack sleep? The most obvious symptom is extreme daytime sleepiness. Other symptoms include the following: 
difficulty learning new concepts
inability to concentrate or a "fuzzy" head
lack of motivation
increased appetite and carbohydrate cravings
reduced sex drive
Sleep deprivation effects
When people don’t get enough sleep, their cognitive functions slow down – making it harder to retain memory and learn. They also experience moodiness, weaker immune system, and impulsiveness.
Other effects also impact the following:
Body weight. Leptin and ghrelin are hormones that tell whether your body is hungry or full. Lack of sleep alters these hormones’ function.
Insulin levels. Sleeplessness also triggers the release of insulin, which may lead to a higher risk of type 2 diabetes.
Hormones. Lack of sleep can also affect growth hormones and testosterone, which in turn lead to symptoms of reduced sex drive and stunted growth.
How to COPE WITH sleep deprivation: TIPS FROM A NAVY SEAL
John McGuire is a former Navy SEAL, and he shares how he survived the grueling Hell Week in this article. 
Get your head in the game
McGuire believes that no matter how uncomfortable you feel from not having enough sleep, the best thing to do is to FOCUS.
“You can’t lose your focus or discipline.”
Put the oxygen mask on yourself first
McGuire says that the key to coping with sleeplessness is organization. The more organized and systematic you make your life, the more you can sort your life out.
Look after yourself first, before looking out for others.
“It’s like on an airplane: You need to place the oxygen mask on yourself first before you can put one on your kid.”
Know your limits
Lack of sleep can make one impatient, lead to stress eating, and lethargy. There’s no harm in embracing your limits.
“A good leader makes decisions to improve things, not make them worse. If you’re in bad shape, you could fall asleep at the wheel. You’ve got to take care of yourself.”
Erectile dysfunction. In combination, those are two of the ugliest words known to man. But can caffeine help you get it up?
Science hasn't found the definitive answer to this question, but one study concluded that fewer men who consume caffeine have problems performing. The study said:
Caffeine intake reduced the odds of prevalent ED, especially an intake equivalent to approximately 2-3 daily cups of coffee (170-375 mg/day). This reduction was also observed among overweight/obese and hypertensive, but not among diabetic men. Yet, these associations are warranted to be investigated in prospective studies