There’s a man who is held prisoner on an island, captured by raiders in his private boat I think? I remember one scene, where he attempts to swim out of the Island but swims into a swarm of Jellyfish. He is saved by the islanders and nursed back to health by a woman who seems to take sympathy on him

Any ideas?

Could be The Island (1980)

I’ll check that out.

I checked descriptions and it has scene with jellyfish.