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My dad was a doctor on a small island, for a year. The islanders dived for sponges and pearls. They couldn't afford a decompression chamber, so if someone got DCS (after freediving too long) they dropped them off the side of the jetty with an old diving helmet, and a friend to keep them company, and pumped air down to them as they gradually re-ascended. Apparently it worked OK.

On the other hand, think about it. With a SCUBA tank, you are taking many breaths under high pressure. With a single free-dive, you only take one breath. With many free-dives, you take many breaths. Is it surprising that repeated deep free-dives cause DCS?

So, it's not a problem if you dive once and go home. But it is a problem if you dive again, and again, and again.

Makes sense.

Depends on how deep you dive and the time you spend down there. for instance, people that attempt world records in freediving might need some decompression time after the dive.