questions

[freedivernd]

Shallow Water Blackout (SWB) happens most to divers who have gone very deep.. 100+ feet (I hate to put a number here) or have spent too much time at shallower depths and on the return to the surface pass out, usually somewhere between 0-30', hence the term SWB (remember, that air in your lungs that has been compressed at depth is expanding quite substantially in the last 30' to the surface), it can also happen within seconds after a diver has surfaced. It's the state of hypoxia (lack of O2) where your body shuts down to save the brain and other vitals. Several factors can increase the chances of that happening.. not being well hydrated, fatigue, sickness, being too competitive (pushing your limits).
Most all serious trouble from SWB can be avoided by following one simple rule when diving - Have a buddy. A buddy can get you to the surface and that's where the air is.
That's it in a very abbreviated explanation.
Fred