Infection with the Lyme bacteria can cause this sort of internal vibration - a type of paresthesia (peripheral nerve sensation). When it's mild, you may first notice it at night when your body is quiet and still.
The supporting cast features James Caan as the young gambler, Charlene Holt, Ed Asner, Paul Fix, Arthur Hunnicutt, Michele Carey, and Christopher George. El Dorado was filmed on location in Tucson, Arizona and Kanab, Utah, and was shot in Technicolor. The paintings in the credits are by Olaf Wieghorst, who plays Swede Larsen in the film. The musical score was composed by Nelson Riddle.
The film follows two con artists, who after winning the map to El Dorado escape from Spain. After being stranded on the island, they use it to lead them to the city of El Dorado, where the people mistake them for gods. Released on March 31, 2000, The Road to El Dorado grossed $76.4 million worldwide on a $95 million budget.