The Navy SEALs made it famous.
But honestly: the Americans did not invent it. The ex-SEAL who made it known got it from yoga. Yoga calls breaths of equal length sama vritti, and the Yoga Sutra describes measured breathing and holding at least 1,600 years ago. So the yogis got there first. Without the helmet.
Source: Patanjali, Yoga Sutra 2.50.
What is box breathing?
Count four in, four hold, four out, four hold. All four sides of the box are the same length. Four rounds take 88 seconds.
That was the plaster.
Breathing gets you through the moment. If something keeps coming back, clear it out with a Guide.
Already worked with a Guide? Then you know how it goes.
The other four.
If you get dizzy, stop and breathe normally. This does not replace treatment. Serious crises belong in other hands.