I would say that the risks are as follows;
1) The damage you get if you fall (lie down, stupid)
2) Damage that might occur due to some unknown inherit malady which is triggered by low oxygen/high C02 etc
3) And the damage of low oxygen levels.
None of these has to do with actually beeing ALONE.
About number three we dont know much. During our breathholds we reach lower levels than most sleep apnea patients but not as deep as stroke patients.
I was part of a test where a scientist was looking for bad effects of low oxygene.
I reach very low levels but still he could not see any long term bad effect of that one breathhold.
I dont know about many BO year after year - what that could do to you.
I was very surprised WDAF about you seeing artificial respiration beeing performed on a BOd freediver. My guess is that it was not necessary - the good old "blow-tap-talk" would be more than enough, I think.
WDAF you seem to be very worried about swollowing your tongue. Why is that. When you BO - other levels of conciousness take over, these subconcious levels are probably a lot smarter than your concious levels and they would never do such a stupid thing as swallowing your tongue. It was actually your body that BOd you to stop you from dooing such a silly thing as holding your breath.