Divers' Cemetery

Just 10 kilometres from one of the most popular tourist cities in Egypt, Red Sea hides one of it's many wonders - a place which every diver should visit at least once in a lifetime. Blue Hole is a submarine sinkhole with a maximum depth of just over 100 metres. There is also a 26 metre long tunnel known as "the arch" whose top is at the depth of 55 metres which leads to open sea. While being one of the most popular diving spots in the world it is also said to be one of the deadliest and most dangerous ones. The Egyptian authorities report over 40 deaths while unofficialy the death counter rises up to even 200. The sinkhole isn't dangerous itself - it doesn't exceed recreational divers' limits. But "the arch" does - it's dark, hard to locate and disorientating. It's the place where most of the divers diving in Blue Hole lose their life. 
The most famous fatal accident is that of Yuri Lipski - a 22 year old diving instructor who died at depth of 115 metres. Yuri took a camera which first filmed his rapid descent and then him drowning to death while trying to ascend. The next day, Lipski's body was recovered and the footage was dicovered. It was given to his mother. 

Years later, Tarek Omar said : "If I had known the footage existed I’d have flooded it. I think the thing that really upset and saddened me about it was that his mom has it now – she has the footage of her own son drowning."

Source: http://www.cairoscene.com/LifeStyle/Egyptian-Diver-Tarek-Omar-The-Keeper-of-Dahab-s-Divers-Cemetery

SORRY FOR THE DELAY :((

Nitrogen narcosis - diving while being drunk?

Nitrogen narcosis - the name explains it. It's a state of mind which is caused by breathing nitrogen at high partial pressure. The effects become noticeable at a depth of about 30 metres and become more hazardous when diving deeper. Diving beyond 40 metres while breathing air (which consists of 78% of nitrogen) is strongly dicouraged by most proffesional organizations. Narcosis may be comlpetely reversed by ascending to a shallower depth with no long-term effect.

Nitrogen narcosis has an an anesthetic effect on diver, similar to being drunk.  It may cause a diver to feel either euphoric or stressful emotions which can affect rational judgment and therefore be very dangerous. It also slows the diver's reaction time, thinking and an ability to reason. There are even recorded cases of underwater hallucinations!

While it's impossible to develop tolerance to nitrogen narcosis, proffesional divers learn to partially cope with the negative effects. When diving beyond 40 metres various mixtures of breathing gases are used - such as trimix and heliox - which replace nitrogen with non-toxic helium.

source: https://www.thoughtco.com/what-is-nitrogen-narcosis-2963052

The Art of Freediving

Freediving is an extreme sport where people dive without any equipment (except fins). Freedivers stay underwater for as long as their trained lungs let them. The official breath-hold record is 11 minutes 35 seconds an the record for the deepest breath-hold dive is 214 metres. This may sound scary, but suprisingly freediving is all about being calm and relaxed, because thats when your body uses the least oxygen. Learning to hold your breath for such a long time requires a lot of training and dedication. Of course natural predispositions like lung capacity, weight etc. can help a lot but what matters the most in every sport is how much are we able to sacrifice for the sake of being the best.

When holding our breath for some time we start to feel the urge to breathe in. Most people think that it is because of lack of oxygen in our body but it's actually our CO2 levels rising. Even when you think that you have to take a breath, it's wrong - You still have a lot of oxygen in your muscles, tissues and blood. The actual when holding breath discomfort comes from the CO2 piling up and the need to ged rid of carbon dioxide from our body. That's why freediving focuses mostly on learning to tolerate the high levels of CO2 in our body.

Read the full article, it's actually very interesting and probably a little bit better than mine.

Source: https://www.theguardian.com/lifeandstyle/the-swimming-blog/2013/sep/16/freediving-body-capabilities-swimming

Sorry for the delay :(