Prudence (1970)

In the near future, a technical diver couple, Ina and Claude, join the crew of an underwater drilling station on a mission to stop a cataclysmic oil spill. While working cut off from the world in extreme conditions, the onboard doctor is infected by a parasitic worm. One by one, the crew members are infected by this tapeworm, which exacerbates its host's most extreme impulses, feeding off their endorphins like an emotional vampire.