Yes "the bends" can be deadly.


When diving, the nitrogen in your air supply is forced into your body at high pressure and gets suspended in your blood. If you lower your pressure (by ascending to the surface) too quickly then the nitrogen comes out of suspension and begins to form bubbles. Those bubble can pop blood vessels, nerves, and even your spinal cord. The trick is to measure your time at depth and calculate how much nitrogen is in your system. You can then use a computer (in your pre-dive planning) to figure out how quickly/slowly you can come to the surface sop that the nitrogen doesn't come out of suspension but gets metabolized at a normal rate. It's pretty safe but you have to know what you are doing and why you are doing it... thus the certification required to dive.


Where people get into trouble is if they do multiple days of diving and build up a lot of nitrogen in their system which will of course get respirated out over a day or two... but if they go flying soon after diving, then the pressure on their body is lower as they climb in attitude, so some of the nitrogen may come out of suspension. Again, usually not a problem if you plan your timing so this doesn't happen, but if you have a lot of nitrogen in your system and you get into an airplane and you lose cabin pressure at high altitude for whatever reason, it could be instant death.

This is why the guidelines are not to fly within 12, 24, or even 48 hours after diving, depending on how much diving you have done, what depths you were at, how long you were at depth, how quickly you ascended, etc. Again, there are easy computers that run these formulas and tell you what is and isn't safe to do.

Hope that helps explain some of it.