"Home From The Sea", the fourth season opener of Magnum, p.i., as described by TV Tome:
It's the 4th of July, and Higgins is playing in a polo match, T.C. is taking his baseball team to a professional game, Rick is out with his latest girlfriend on the King Kamehameha II yacht, and Thomas is observing his annual Independence Day tradition of a solitary day at sea -- until his surf ski is capsized in the wake of a recklessly driven speedboat and set adrift. Carried off further and further away from land by the powerful Molokai Channel, Thomas relies on childhood memories of his father's training him to tread water to keep himself afloat as he struggles desperately to stay above water and fend off a menacing shark. As the hours pass, Higgins, T.C. and Rick each have a sixth sense that Thomas is in trouble, and they team up to rescue him. Thomas approaches the twenty-four hour mark in the water recalling his wedding to Michelle and his father's burial -- on July 4, 1951 -- as Higgins scoops him out of the ocean, with T.C. in his helicopter overhead and Rick on the yacht nearby.
So while you and Cal may be mad, BiLly, your memories of this episode are not a symptom of that madness.
As I remember, this was an excellent episode, but then I would say that!