What Causes Sudden Loss Of Consciousness?
A heart arrhythmia or seizure must be considered.
Detailed Answer:
I read your question carefully and I understand your concern.
That episode you describe must be investigated after. Judging from your description there can be two most likely origins.
The first is a heart related cause, transitory heart rhythm disorder which led to not enough blood pumped from the heart and as a result the brain suffering as well leading to his loss of consciousness.
The second possibility would be the possibility of a seizure.
So to look for heart issues an EKG is the initial exam, followed if it doesn't reveal anything by a 24 Holter rhythm study (carrying a portable device registering heart electrical activity over the 24 hours) and possibly a heart ultrasound.
To investigate for seizures an EEG (electroencephalogram - registering brain electrical activity) is necessary as well as imaging tests (CT or MRI) to look for seizure causes such as tumor or stroke for example.
Some routine blood tests for blood glucose and electrolytes are also necessary to exclude a metabolic origin.
Of course not all these tests are done all at once, it is progressed step-wise excluding the most common and urgent causes, if normal is progressed to the rest of the tests. The initial tests should be the blood tests and the EKG since they are cheap routine tests and the heart possibility would need the more immediate attention.
I remain at your disposal for other questions.