Chiba has two reasons for taking up dancing -- to exercise his legs and because he always wanted to but was prevented by the war.  But really, I think he does it because he's lonely and doesn't feel loved.  This is also shown by his obsession with his dogs and even with his anger when his wife criticizes his car.

I believe that the circumstances of his mother's death and divorce both make Chiba feel guilty.  He was out partying when his mother died and that makes him feel so guilty he actually welcomes the idea that he might be prone to strokes like she was.