I'm too busy to go BOWLing with my compadres, so my heart is dying inside.
|NO TIME LEFT
|BOTTOM OF YOUR HEART
Both kanji are"heart + dying," but, in busy (忙). . .the heart is on the LEFT, because you're so busy you have no time LEFT.
With forget(忘), the heart is on the bottom, because you are apologizing to your boss FROM THE BOTTOM OF YOUR heart for forgetting to bring the report to the big meeting.